The problem for me with bbPress themes, is that they are totally different than WordPress themes. So, it's not like you can just which from blogging software (WordPress) to forum software (bbPress) and create themes for each. I've looked into developing bbPress themes, and it doesn't appear to be any more difficult, rather just different and less motivating (due to being less popular).

While I think it's a good idea to develop a bbPress in a theme community. I think having it as a replacement for theme competitiveness is misplaced, that is, if I didn't misunderstand you. I think there a quite a few WordPress theme developers, that would like to develop bbPress themes, but haven't found the time (myself included). This looks like the chicken or the egg problem. bbPress needs to be popular to attract developers, but people aren't going to come if bbPress and bbPress theme aren't developed. I think bbPress will pick up speed in several months. Hopefully your project gets a bbPress theme out the door, then bbPress will be that much more attractable.