I agree, variant are interesting to give another flavor to a class. We already have the Savage Bard and the paladin are interesting in my opinion.
The domain wizard told earlier in this thread is just a no brainer. It is more powerfull than a specialist, as you have no prohibited school, but it is more powerfull of a generalist, because of teh bonus spell he knows at each spell level and the extra spell he can cast. If someone would propose it like that, I would tell it shouldn't be approved.
But making one based on the towers could be very interesting. It would be interesting to see a variant for teh six tower, but I can hardly see what could be done for the positive tower (negative is not too hard, it is called a necromancer

)
Also, the variant should not have a number of spell per day like a sorcerer, as it is written up here in teh base class submitted.