Just a point: A DM has a choice of what races he/she allows in the campaign... So, why couldn't Paizo come out with subrace books? I mean, if you don't like the idea of subraces, you don't have to use them in your campaigns. In my opinion, the only thing adding those subraces would do is add another book (at least some)people would be willing to pay money to Paizo for, thereby increasing their profits. Why is this a bad thing?
