There's nothing to stop a Qt port to MorphOS or AmigaOS; the basic class structure, would translate VERY easily to a BOOPSI-based (method/dispatch) and Exec Device (commands via DoIO()) framework. Qt bears a good resemblence to MUI enough to even layer on top of that.
What you'd get on Qt however is a complete loss of some of the more advanced features; MIME clipboards and so on.
I don't know how many Qt applications rely on them, you would have to find an app to port as a test
