Wow...welcome to 3 years ago, man. preloader allows for exactly that (priiloader expanded on that). I haven't seen the original system menu in months, and haven't used it as a main source in...about 2,5 years now. What I did use instead kinda varied (GX, then CFG, then wiiflow, switched to uneek and finally neek2o + postloader), but I think you'll find it hard to come up with something that's not already possible. The only reason I ever used the system menu in that time was because of the game options, and most of the important ones are now possible via settings editor GUI.
It's certainly feasible and not oversimplifying at all. If you know how to write a GUI that runs things, you can make it an autoboot on your wii (in more than one way, postloader is exactly that: a launcher of wii games, gamecube games, channels and homebrew).
It can do that, but it can't launch backups from a cold boot (Not the system menu or PostLoader). You have to run NeoGamma to do that, whereas what I had in mind, you wouldn't even have to touch the app at all (Just start up the system and insert your disc, go to the disc channel and start it from there). But if it seems that people can make system menu hooks that can run from a cold boot, then I have to wonder why there isn't a whole lot of support for them.
Yes you can. With postloader, I can start a backup wii game with 2 clicks of my wiimote. Including one to activate said wiimote.
For backup discs, it's pretty much the same thing, though I don't think postloader supports it yet. CFG, GX and neogamma do, so you can just cold boot into those programs.
Perhaps you don't really understand how priiloader works: it doesn't use "hooks" to change the system menu. It
totally replaces the system menu. The real system menu gets moved to another spot in the memory, and all priiloader "really" is, is a very simple GUI that is generally designed to only show up if you hold reset while booting your wii. In all other cases, you will set it to load something else immediately. Something like the real system menu, bootmii, the homebrew channel or a fowarder dol. And that last thing is exactly what you need: a forwarder dol to your favorite piece of homebrew.
As such, I don't really get what you mean with "there isn't a whole lot of support for them"? Postloader has
127 pages of development, and that's just for version 3. The other loaders usually have over a thousand.
Maybe it's more correct that it doesn't
need support: it is already working flawlessly. All that was missing was someone who wrote a GUI that could load homebrew, channels and wii games*. And then stfour came along and built exactly that.
So...I don't really understand what you're asking for. Why mod the system menu to look different if you can already write something completely different that can do everything the system menu can and more?
*I should give props to GX for already doing that...however, it never quite worked that well for me.