The problem is, once Zen is out, Bristol Ridge will be a lot less attractive. Raven Ridge is supposed to arrive a few months after Zen, right? People who want an APU will think twice about buying Bristol Ridge when Raven Ridge is around the corner. Meanwhile, people who want an APU now will think twice about buying current ones when Bristol Ridge is already on the market, just not available for DIY builders.
So AMD's strategy in the APU market seems to be anti-DIY. That may be either from assuming that's it's a small market, or because AMD doesn't believe that Bristol Ridge is truly attractive. Of course it's also possible that the problem is just getting the motherboards out.