However, a major downside to this setup is that if I close the apps, the setup disappears. That is, my setup uses multiple distinct apps that are connected together (directly, or through the MIDI and Audio routing apps) and there's no way to persist this multi-app setup between sessions, so any time I have to set it up from scratch (because I closed the apps or rebooted the iPad), I lose all at state and have to set it all up again from scratch.
Until that is solved, I don't think I'd really count it as a serious setup. It's an incredibly powerful toy though!
Of course, this applies to an iOS-only (or iOS-centric at least) setup and not what it sounds like you're referring to: using iOS as cintoellets for an otherwise laptop/desktop-based setup. I imagine that has fewer of the above issues.
Speaking of musical interfaces, Fugue Machine is practically perfect. I just wish you could have a longer loop length.
Although part of the problem is that, beyond the router state, there is configuration data spread out between the different apps (e.g. Some midi stuff setup in Gadget or whatever), so we will see how much it helps. Hopefully you're right!!
Does anyone know if that's possible on a touchscreen PC/tablet running Windows?
I just tested this on my Win10 tablet; I could indeed poke at the control panel app on one side of the split screen while manipulating Chrome on the other. I can't vouch for any other apps, or for running Win10 in 'desktop mode'.