A quick update on our progress:
The first item in my original post “Update Unity’s fork of Mono to the latest code from the upstream Mono repo” has landed internally now. It will appear in the upcoming public Unity release 2021.2.0a18.
This work doesn’t have user-facing changes (outside of bug fixes), but it does lay the foundation for much of the other work I mentioned.
I’ll continue to update that original post and this thread with details as we know when other parts will land.