my opinion is based on 2 points:

1) from nokia press release: "The acquisition of Trolltech will enable Nokia to accelerate its cross-platform software strategy for mobile devices and desktop applications" ... "With Trolltech, Nokia and third party developers will be able to develop applications that work in the Internet, across Nokia's device portfolio and on PCs"

so nokia wants to spread qt everywhere, why would they left tablets behind?

2) why would they support 2 different toolkits on one small device, that is memory (and cpu) restricted. further more, as i see it, nokia prefers to control the design from hw to sw. they could not do it with gtk, they could do it with qt.

what's for sure, transition of maemo to qt would be painful for 3rd party apps, maybe impossible. just look at problems switching from os2007 to os2008, that should be relatively straightforward.