Perhaps I'm missing something, but can't you get all the benefits of a belt drive with a chain enclosed in a full chaincase [very low maintenance] at a much lower cost?
I'm sure with current plastic tech you could produce a very good chaincase for pretty cheap. Fitting a chaincase on the other hand is always going to be a bit of a fiddly operation. I wouldn't be surprised if the assembly costs of fitting a chaincase is a big reason trek are using belts.