RA does have PROPER PIXEL SHADER SUPPORT.
If you want the precompiled pack google for filthy pants blog.
That said the GPU is quite weak but yeah it can do some basic shaders just fine.
I don't think any recent changes are prone to be WiiU breaking anyway.
The biggest issues I see on WiiU are:
- Slow I/O, asset downloads is terrible, and so is the core updater, also scanning, not sure this is something RA can fix directly.
- Stutter while starting with retroachievements because of the issue mentioned above (downloading achievement badges is not properly threaded I think)
- No resolution changing support (I'd like to be able to switch to 480p when using the gamepad, and to my TV res when using the TV so scanlines look better)
- Netplay doesn't work properly with relay enabled
I think that's it?
(dynarec bounty doesn't count, cores are a different thing)
The reason Wii port is in such a sorry state (if that's even true, I no longer have a Wii so I haven't tried) is because someone made some improvements and never really bothered with bringing them back upstream (which is the reason the improvements are not really there in the first place). Recently Wiimpathy has added quite a few fixes and RGUI has gotten a lot better so it should be fine.
Just for those who haven't seen this: