I wonder how the transition to Qt in Maemo 6 will work out in practice. We know GTK+/Hildon won't be removed, but will the new Qt-based touch UI layer build upon this impressive base in Maemo 5, sharing as much code as possible? Or will there be a parallel Qt implementation of the same concepts -- superficially similar, but internally entirely separate from Hildon?
Perhaps the likeliest outcome will be akin to Carbon vs. Cocoa on Mac OS X. The two will track each other for quite some time; some components in both APIs will be implemented on top of the other as deemed appropriate; but it's inevitable that the platform owner will eventually make a clear stand for the API that's better aligned with their overall goals and whose development they control more tightly. (Mac OS X's iPhone fork was the final nail in Carbon's coffin, and the political preference for Qt across all of Nokia's platforms will eventually kill Hildon.)
Perhaps the likeliest outcome will be akin to Carbon vs. Cocoa on Mac OS X. The two will track each other for quite some time; some components in both APIs will be implemented on top of the other as deemed appropriate; but it's inevitable that the platform owner will eventually make a clear stand for the API that's better aligned with their overall goals and whose development they control more tightly. (Mac OS X's iPhone fork was the final nail in Carbon's coffin, and the political preference for Qt across all of Nokia's platforms will eventually kill Hildon.)