Thanks!. I was thinking Regions were a "Copy"GC that one that moves everything into another place of the memory. Nice to see the RefC is custom like that, sounds interesting.
No, all our efforts are spent in the --gc:destructorsmode. There is a new plan for pairing that with a precise copying GC though since both variants seem to work together in combination rather nicely and only require a non-restrictive heap topology. I'm writing a blog post about it... (famous last words)