So here's the thing with icade. Each press of a button activates a key, but releasing also activates a different key. So to use the icade setting with a keyboard, one would have to press a key to flip, and then press another key to deactivate the same flipper. So not ideal.
What's worse is, since you brought up the icade/keyboard idea, I tested it and just realized, iCade will not pair up with iOS 8.4.1.