Right now it is just the foundation I guess. That is, more work to be put on top of it. byroot kind of pointed that out that the proposal reminds him of containers and I think this is the long-term goal eventually, e. g. namespaced isolated containers. At a later time, I think, the syntax for refinements may be simplified and also be integrated into Ruby::Box, since Ruby::Box is kind of a stronger refinement in the long run. But that's my take; ultimately one has to ask matz about the changes. What he did say on the bugtracker was that this is to be considered a low-level API e. g. a foundation work. So things will be put on top of that eventually.

To me it seems very few people use ractors. A bit more use fibers though.

It's a bit of a mess IMO. I'd much prefer everything be simplified aggressively in regards to threads + GIL; and Ractors integrated on top of Ruby::Box to provide not only namespaced container-like entities but also thread-support as a first-class citizen at all times. The API of ractors is weird and really not fun to use.