I agree with Baard. Fort Joy island desperately needs more fights. A voidwoken assault sounds good, and it would also serve as a sort of prelude to the Voidwyrm attack - it could be a way to prepare you to the hell that is Voidwyrm environmental effects.
Another (prompted) Magister fight would also be great. How about the Magisters find the Seeker camp and assault it, which then prompts Gareth to up his own timetable and assault the Magisters at the beach?
Voidwoken attacking the fortress itself... well, I'd say, if it's possible to make that happen only if you kill all of the Magisters in the fortress... then I'd be on board. Haha, but that is a whole lot of qualifiers.
