Concurrency is always hard and fibers could be interesting, but looking at src/runtime/gravity_vm.c It appears to be single threaded with max 1 fiber running simultaneously per VM.

I think there is still a niche for something like a Lua/Erlang hybrid where there is a real possibility that the VM will run high level code units on multiple cores.

The other thing missing from Lua and LuaJIT which would be nice in future VMs would be support for SIMD vector optimizations.