Acceptance is likely due to Ian Taylor being a long term GCC developer who is easy to work with, which mean that 1) the front end obeys the often unwritten conventions for good behavior, and 2) they know Ian Taylor will be around to (and capable of) fixing the various unavoidable problems that will show up. Thus, the new front end should only put a minimal burden on the other maintainers.

The merit of Go itself has likely been less of a concern.

What does this mean for go exactly? Sorry for my ignorance. Does this mean that go will be distributed with GCC going forward (once the merge date is determined that is)?

I think that's right. But as they stated, they're not sure when the merge will take place.

This makes me wonder a little bit if LLVM won't (maybe?) do something similar. Not that it's a 'huge' deal, but for parity?

Apple's investment is in ObjC; I don't see them doing any work on Go.