You could, as a stopgap, use the mage. Just limit the spell selections to better reflect the specialist nature and then convert once the specialists are out.
I had considered that.
Someone here (I can't remember who) in a thread (that I can no longer find) went through all the spells and sorted them by Spellbound category and subcategory. That was a really good job but there was one subcategory that had no spells in it and even some of the categories as a whole had only a small amount of spells in them.
It's still an option I'm considering but I don't want it to end up like the AD&D 2E specialists which weren't balanced at all. The Abjurer and Necromancer were poor options until you gained access to high level spells (and the Cleric actually made a better necromancer type anyway) whereas being an Invoker, Conjurer or Transmuter were clearly superior choices.
Also, I'm reluctant to start the campaign with absolutely no knowledge of how long I'm going to have to wait before release; it could be 6 months or over a year. Considering the consistent lack of updates I'm guessing that it's not likely to be out within 6 months (and, at this point, that would still be too long of a wait). So it's probably going to be Pathfinder, since everyone has the free Beta version at least, and hope for the best. But I'm guessing it's going to stay Pathfinder as by the time the Spellbounds come out, it's extremely unlikely that my players will want to switch systems; especially after putting the game on hold for a year and a half as is.