Albeit in a probably less cohesive structure, my memory from the start of the GBA upwards. While I have no favourite in cards my memory is more geared towards EZFlash equipment as that is what I spent the most time around.
So to begin.
First era: rebadged GBC carts. Speed hacks and other nonsense. (Emulation was pretty good by this point, certainly playable level)
Second: Stuff like the f2a, EZ1/2, XG flash (the big thing was the introduction of USB here: previously people used parallel ports)
Third: EZ3, SC and co. Pretty much laid the way for the early DS cards. And formed the basis for the use of NAND and a fast section of memory approach (previous cards used NOR memory which is a pain to work with: expensive and small for it,
Mirroring the later thing with DLDI carts that could use the pogoshell got a boost in sales to an extent although that was pretty much over by the time the DS appeared.
DS era begins
The DS appeared or more specifically the passme, for a few weeks (months?) forums were littered with "how do I run DS roms?" to which the answer was "you can't and I do not know if you will be able to, unless they magically are able to come up with DS carts which may not happen as stuff needs to be small" (words now eaten on my part)
Then came neoflash (a rebadged XGflash as I recall) and the buying spree of those, }{ain/Kain's patcher and later loadme (which aside from a few standalone patches (tetris and mariokart) vanished before the vaunted 2.0) provided a rather buggy entrance (Advance Wars did not work for the former) as well as the introduction of DS patchers for existing cards (While others were doing good work Supercard really came into their own here: in many regards it was who cares about GBA when you have DS and they were cheap too courtesy of the cheap memory (which is why the GBA was less than brilliant)). There was also a bit of rom ripping going on (see the link in my signature) to get more on there or even to make them fit in the first place and perhaps formed the basis of early rom hacking on the DS (the odd sound hack/swap, level swap, text swap, video swap, sprite swap appeared)
The Passme2 arrived to counter new protection (albeit rather awkwardly), wifime sank and flashme was king.
Then came the DS intended carts: EZ4 (my cart to this day) the M3 and G6 (I remember the G6 was once the (very expensive pinnacle) of DS roms, if only by two or three roms) as well as the SD Supercards. In some regards they are little more than the previous cards with a lick of paint (the EZ4 is very similar to the EZ3 and the m3 and all that changed to SD or smaller from CF). A minor tweak for stuff like the SC rumble, M3 pro and EZ4lite compact and lite sized cards (which pretty much cemented microSD as the weapon of choice). Neoflash were pretty much a running joke now courtesy of them dumping their first cart in rather spectacular fashion (their later cards while not perhaps up there with the major cards.
The m3cf and SCCF as well as the more homebrew oriented GBAMP garnered a major lead thanks to having read code (and later write code) for homebrew (even if most stuff still used GBA era filesystems). DLDI (and the moonshell concept it appeared from) wiped this from existence in December 2006/January 2007 (the situation also made a minor comeback with the browser patches from triforce)
Patching varied from fire and forget to fairly complex ( Works with Safe Mode, Trim or 4x DMA, Force R/W, Trim.) See
http://gbatemp.net/?showtopic=38530 and any of the early rom topics for this one.
Somewhere in all that Mr Korth promptly arrived and the nopass was born in the form of the max media launcher (it was shortly before the launch of the EZ4) and shortly afterwards every flash cart company under the sun.
Clones of various carts (mainly the supercards) appeared including the first foray by team cyclops.
Shock horror DS slot carts appeared.
Again a bit of a frenzy (especially on the DSX front) before the old stalwarts appeared.
M3 (and the presently insanely popular R4 which if popular rumour is to be believed are OEM M3s), The G6 appeared a bit later but was somewhat outshined.
SC one
EZ5
The latter 2 were overtaken by the rapid updates of the r4/m3dss and some poor choices in some regards and somewhere in there the first acekard appeared with AKFS so did not make too much of a dent beyond the initial week or so.
Ncard (pioneered to an extent by the GBA era people behind GBAlink (had to look that one up despite me using their lists for Chinese GBA names)) also garned a following for being solid, cheap, if rather basic cards.
Team DSX went AWOL and the R4 people also slipped a bit (the whole arm7 thing) leaving the door open for what I do not consider the next gen but certainly new competitors.
Team cyclops came back with the CycloDS (and while not specifically relevant here a wii chip)
Acekard came back with a fully open source card (various companies had released various bits of source as far back as the EZ3 but this was the first truely 100% open source card)
And a couple of weeks back the DSTT/TTDS (one of which is a neoflash product)
Also somewhere in that came the tit for tat battles:
compatibility was near perfect so nobody minded much here. The ARM7 fix and EZ5 savelist (meaning to an extent the arm7 situation was dodged) perhaps the most notable points during this one (neglecting the initial DS slot offerings).
download play was first (flashme did not have an uninstaller that worked for lites and DS slot so people did seem to care for it much)
next features.
soft reset reared its head although that was a bit of a formality having existed in the DS via GBA slot times.
cheats seemed to be the first up (while they had existed for quite a while in some forms flash carts were new)
Then the SCONE made stuff like savestates and text viewer (very impressive to me)
GBA games were also wanted and the EZFlash 3 in 1 appeared (as well as perhaps more importantly the source) meaning GBA was back on the table. We are now starting to see competition on this front too. (For what it is worth I sat back and smirked as it did not bother me)
Pokemon linking (either to GBA or to Wii) showed its head but it did not seem to matter all that much.
Today we have come full circle (again) and bootup time is the concern and SDHC is edging in there as prices fall (I remember shortly before DS slot carts appeared 2 gigabyte microSD carts were obscene sums while 1 gigabyte cards were almost throwaway).
I have missed a lot of stuff out but it is just my memory of it all. Perhaps the biggest point for me is how cheap it has become (I remember paying about the price of 3-4 GBA games for my 32 Mbyte EZ2 and thinking I got a bargain whereas now people can get a near flawless cart for less than the price of a retail game although this can be offset somewhat by the presently high price of SDHC carts).
Just because it matters to me rom hacking on the DS is now almost up there with the 8/16 bit era stuff, only really let down by emulation (desmume and no$gba are good but they are nowhere near the GBA, snes, nes or even PS1 level) and to a lesser extent assembly (documentation, tools: to my knowledge there is no decent DS tracer).
Homebrew on the other hand has reached new heights (maybe not on the emulation front) but wifi and touchscreen has led to some fantastic applications (Urza's recent list is a good starting point), protocol implementations (FTP, countless chat apps including some very polished ones, linux, email, internet, audio and even a bit of video).
The question is finally answered
Essay over: to answer the original question a new gen of carts?
The DS slot has peaked in my opinion so once features get to the same level (which they are more or less) and SDHC becomes standard (7 months is my guess until it will be unusual for a cart not to do it) I do not think a new gen will appear until the successor to the DS appears.
The big names might come out with a new version if only to consolidate features or for financial reasons. In my opinion the days of integrated memory are over but we may see a few add a small section (maybe 128 Mbytes).
The next big feature battle (real ones rather than bootup speed)
Maybe wifi based adding of roms (how many of you with a modded xbox have not used FTP) and maybe a minor scuffle on the GBA front (I like the 3 in 1 and ewin but they are a bit basic and could stand to be expanded).
GUI front
Team DSX tried it but it did not stick (although that can quite reasonably be attributed to other reasons in my opinion), moonshell is nice and I hope the carts that use it stick with it and maybe even a few more pick it up. I do not think we will see that much on this front (i.e. the creation of "replacement dashboard"/XBMC skins calibre stuff) other than maybe a tweaked font/layout/rom name handling. People seem content with having a picture, arrows and few icons of their favourite anime characters/film star/TV series/game series/porn star/place in the world/family/pets/beer
Open source front:
It would be nice I think but I find people wanting to work on the loader beyond tweaks/fixes not so common but those wanting to interface their software to the device more so (see all the write code and DLDI hassles). This means more example code, libraries and specs/documentation released. No bad thing in my world as "reverse engineering" source to get the interface/what is done down is not the favourite activity of too many people.
Homebrew: tilt sensors, rumble (to a lesser extent), ram, coprocessors (perhaps: although I know it is marketing speak the DSX FPGA could have been interesting), extensions (think DS Serial) have appeared but aside from ram and maybe tilt sensor (they have been a notable part of some homebrew contests) nothing has been taken advantage of. Perhaps wii interface could form the next step but that is probably outside the purview of flash cart makers.
I would like to see replacement firmwares take off but that is a different topic.
