Are we talking about "PEP 554 – Multiple Interpreters in the Stdlib"[1] proposal?
Yes and https://peps.python.org/pep-0684/ which is no longer a proposal, but it's also been implemented in CPython 3.12.
with PoC of the parallelization code being developed here https://github.com/jsbueno/extrainterpreters
But I have the same question as you have if we add another coming concurrency model: SubinterpreterThreadPool, which will be possible with the per-interpreter GIL in python 3.12 and later.
That's another new model that is already confirmed to be coming: interpreters (isolated from each other) in the same process, that can run with each their own GIL.