Changes in the D2 design to help the GC?

[Lutger]

I'm worried too about this, but haven't a clue as to what is needed to 
overcome the performance gap. I don't think extending the type system in a 
major way for some extra performance is worth it. Still, there may be some 
ways to make less drastic adjustments so that a (more) precise GC can be 
built. Or to put it another way: to not make a high performance GC for D 
impossible in the future.