Moving GC

[dsimcha]

I've been playing around with custom memory allocation schemes for some
programs, which are based on regions.  These work great, and are significantly
faster for the use cases I'm using them for, than the general allocation
scheme.  However, everything would break if it were used with reference types
and a moving GC because, as far as the GC knows, the regions I'm allocating
from it are untyped.

What are the odds that some D implementation gets a moving GC in the
foreseeable future?  Are they significant enough that I should avoid relying
on the GC being non-moving, or is worrying about such things just overdoing
trying to be future-proof?