Code/firmware/hardware revision levels is nothing new. It is hardly ideal but it has been worked with in the past. We are already seeing the "well it is not going to be any good" notions surfacing -- I am reminded of the discovery of JTAG for the 360, it happened mid year and did not get worked up into something capable of doing commercial games until around Christmas. We saw loads of people stop holding off (it was a good year for games) around September/October, and then there was not a perfectly timed banwave but a good one. It would be a few years before RGH appeared so the amount of whining that went on as people sat there with their banned 360s (and apparently online was absolutely essential for a lot of people thus them deeming them worthless, sadly I never got it together to buy all those banned 360s for nothing).
I have previously pondered what a homebrew/hacking scene needs.
http://gbatemp.net/threads/buy-switch-now-or-hold-off.482813/#post-7551355
Still if you want to defy the odds then
Interesting hardware... it is not really. It is a sort of high end* phone/tablet with a control pad, and not even a great one in the case of the joycons. On the flip side it is not a complete turn off.
*in terms of grunt it is up there, however in terms of architecture it appears it is a sort of "money no object" project about 3 years ago. This is not quite as bad as it was for the 3ds (a really odd 3d setup) and DS (a completely custom 3d setup that you had to learn to handle) but I will note it as part of this.
Power wise I am not seeing it break out of the 16 bit and earlier rut for emulation (mainly as PC has barely decided to drag itself out of that rut), I can see N64, PS1 and gamecube stuff happening in the longer term but straight recompiles is a harder prospect. To that end nobody is likely to keep their switch on an older firmware (more later) for that, and may even look back at their PSP or a raspberry pi or something. If you can get all the usual suspects from that era (offerings from sega, nintendo, atari, maybe amiga and then start on the edge cases) going in reasonable speeds and resolutions (the screen should handle it well enough), possibly with the perk of local two player if you reckon the joycons will manage it you will gain some interest.
Interesting commercial games... despite what fanboys are gushing it is not there and the upcoming releases are pretty barren, as is the commitment from the big pubs and devs, I shall await the turn of the tide on Mario like it did for Zelda (we saw the cracks from the start, I am not sure it will end up as another Sunshine but it ain't far off). The library is not abysmal but yeah... oh and we are paying for online this time as well. If you can get ROM hacking going on for it, and also provide the option to play new games (I am not seeing any great black box type setups preventing you from virtualising the newer loaders, this is not to say you won't have to comb through the code and look for every check and trip they might employ but if a handful of people can do it for the 360 against Microsoft you can certainly take on the clowns at Nintendo's security department) it will help.
Software. Get those libraries, interpreters and compilers in -- as great as the GBA and DS homebrew scenes were you have to remember they were truly good for the time, and as soon as something better (in this case IOS about 2/3 of the way through the DS) came along they were dropped hard. I like messing around with C and assembly but it is not a terribly practical way to write cool applications you just want to have, and while I massively respect those doing the lovingly hand crafted emulators for the GBA and DS when the option arose to half arsed port something written entirely in generic C and patch a bit to get it running then that became the dominant method and one used by most.
Libraries start with SDL which should be perfectly doable (the DS was not quite there, PSP did fine though and the switch should surely be able to handle it), you almost certainly want python, lua will doubtless turn up before long. Java then... the best I can see happening is a workable version of android gets ported and with that comes Java, without that then you could probably get something resembling a real version of Java going on (compared to
http://gbatemp.net/threads/java-for-ds.57263/ we saw on the DS).
From there you can go for the higher level game makers, things like unity and whatever else.
Likewise if you want to port the usual suspects from
http://osgameclones.com/ then do it to it. Alternatively figure out the sorts of libraries such things will need and start on them, or at the very least figure out if any of the code there will need redoing (for quake on the DS it was noted that the DS' floating point options were... not great and that held things back a bit). Maybe also check the popular mods to see if they have a chance of running.
Media is a good thing to have. Don't know if you can get a mplayer port + basic frontend all handling scene style videos (AVI XVID + MP4 H264 + MKV H264 + whatever the cretins in the anime world are doing this week (is that 10 bit nonsense still going on?), though subs to vsfilter grade are a good choice), maybe also an ad blocking youtube player, but that would be my baseline.
Probably pie in the sky but get a serviceable web browser going on and things will be good. You live in a good time for it as web development got nerfed in favour of mobile phones and tablets compared to the DS era which caught the rise of javascript and CSS (+ "rich media" + flash + urgh...). If you can get browser web dev to the point where the high end software development options mean web devs can fart out fun little games aimed at joycons or whatever then that will not hurt.
Mentioned in the early link but
money changed the game entirely. Barring an android port I am not sure what you can get going on for a paid money shop, and adverts would be an odd one to see. If you want to get a download service going on then know most of your theoretical competition (which is to say all the other open source handhelds and such devices) will tend to have such a service.
Frankly I imagine I am going to be looking back at the 3ds fondly for this one (and I did not care for the 3ds) -- give me a nice writeup of your hacks and I will enjoy reading it but I am here for software wherever it comes from, not for the sake of hacking a console.