Hildon, basically a GTK+ extension, stays stable through the Fremantle maintenance releases. Harmattan will come with a framework based on Qt, as announced. If there is a community project willing to bring Hildon further to Harmattan times, that is another story. And before you ask Harmattan will support portrait mode in the way that makes more sense based on our UI vision and the feedback received from Maemo 5 users, our usability studies etc.