This was discussed a couple of years ago with lots of comments¹. I'm unsure how much has changed in the meantime, as the top couple of pages of commits on GH are upstream emacs changes. Would make me happy to see it progressing though, as(like with neovim) the tugs in different directions allows things to be tested out that might not make it past the original mail to a developer list in the upstream projects.
Edit: I decided to have a quick poke around, and there are ~40 non-upstream commits this year. About half of those are minor cleanups and cargo dependency updates.