I would expect a FSF mobile app store to have an impact in the long term, just like GNU took at least 10 years to start being useful for a wider public.
Regarding the distribution issue, I think you’re correct, but that’s much more easy to solve than changing the terms of service. Heck, I think that Google could start doing this very soon if they wanted to, and without going through their legal department: add space annd some UI in the market submission process to host source packages of GPL apps. Without such changes, I believe it can also be tolerated like FSF tolerated for many years the CDs distributed with magazines, packed with binaries and no source.
Note to self: a free mobile market should easily allow for -src packages alongside the binaries, like debian repositories do.
Are you concerned that FSF is putting itself in a corner with this? I am, kinda.