- GC is added after a lot of language is already there.
- Actors are planned to be added _after_ I/O, and _after_ GC, and _after_ all the GUI capabilities (Trello board lists "figure out how to rewrite event loop with actors")
- A lot of FFI is already there, so GC, and actors are coming after FFI.
These are not features you add on top of a language and hope they magically work. Actors directly affect how I/O and GC work. GC should be very aware of how FFI works. etc.etc.etc.
A lot of these issues are dismissed by the core team as "it's not difficult to write a GC, we have it in a branch somewhere" (referring to a naïve mark-and sweep stop-the-world GC).