Maintenance rank 3 no longer unlocks engineer
I would assume the flag that comes from Maintenance is still drawing from the old source, since how he revamped/replaced to old system of Talents. Or it had flags relating to another portion of Maintenance (I would go with the first possibility I said).
This would also apply to Priest unlock wouldn't it?
Probably; I would say it's safe to assume so.
I could still unlock priest in the beta, so I don't think so.
Priest is currently unlockable with staff mastery still
Engineer cannot be unlocked by any means
You should be able to unlock it still by winning a battle with a wrench equipped as your main weapon.