Yes, there is progress. But it is very far from anything you might consider complete or arguably even usable--there's no implementation of malloc or basic stdio, for example.
If I recall correctly from the mailing list when this was first proposed, someone had a use case for custom libc but extending it to a general purpose libc diminished properties that would distinguish it from (e.g.) musl-libc.
Edited to include the link to Scudo: https://github.com/llvm/llvm-project/tree/main/compiler-rt/l...