It would be nice to fix ALL THE PROBLEMS at once, but I think to begin with we might just settle for fixing several big ones, at which other companies have already failed. :-)
If B2G required every bit of software right the way down to be open from the start, it would never ship a phone and therefore have zero market impact. The fact that some bits of the stacks of some phones will be proprietary doesn't mean we think this is a good thing, or that we won't be using various means to try and improve matters.