I can see your point and in fact even agree that this is what should have happened in an ideal world.

OTOH: I am not yet certain about the quality of the "community supported" versions of Qt/GTK. If they are both rock solid, then you get what you want, don't you? At least wo releases in a row that feature both toolkits.
You may even get GTK-support long after Harmattan... Who says GTK is deprecated? If it's there in extras, it can as well be there to stay.

Pulling it in as a dependency may sound a nightmare on current hardware, but who knows how much memory we will have available on Harmattan devices?

So a lot depends on the quality of the "community supported" versions of both toolkits, especially on the quality of GTK in Harmattan and later versions. It can go all wrong... or it could be very easy. What I'd hope for is that one of the other players who currently seem to hesitantly watch Maemo grow (Intel? Ubuntu? ...?) find it interesting enough to get their hands dirty here. "Community supported" doesn't necessarily mean that members of this forum need to do it on a rainy weekend.