Those are all general issues that would apply to developing GCC, aside from compile times and tooling integration they don't effect NDK users. So the question goes back to being specific, why deprecate GCC while it's still popular elsewhere and well supported on this hardware?
A), I think you mean "deprecate", it's been depreciating just fine by itself.
B) If you ever want to make a change to the toolchain, HARD SWERVE on supporting GCC. It's a liability if you need to modify it at all. This may have more to do with what Google wants to support rather than any effect on the end user.
Eddyit: Spelshing.