Absolutely part of the plan! However, in that case I would prefer to turn off the note correction feature (which currently is the core of my idea), otherwise it would feel so weird if you play a certain note and another one comes out of the speaker.
In addition to just MIDI devices, I want to allow users to use anything they can hook up to their computer and that can act as an input device. That would include MIDI devices (there are solo instruments which may be way more fun than a piano style keyboard), but also things like your phone's touch screen via bluetooth (which would probably require an app for the phone). They user would have to "register" their custom device once, and if it is an unknown device type, they'd have to press all its keys or slide the screen or whatever, so that the game can make use of them.
If and how and for what platforms that is feasible using Godot remains to be seen. There may e.g. be limitations on the web platform, although for MIDI devices, there is the Web MIDI API.
But before going there, I'll have to work a lot on the musical and visuals parts of the game...
