Looking through recent Discord discussion:
We are looking to release 0.12 soon with PDF/A support and build on that for 0.13, which is the target for tagged PDF, not neccessarily PDF/UA-1. Note that /UA-1 compliance cannot be achieved fully automatically, we need some input from the users as e.g. what do your pictures show, what role a figure plays, and more.
– @reknih, 2024-09-13T22:00:00Z; on Discord
And there is a freshly open PR: Minimal PDF/A support by laurmaedje · Pull Request #5075 · typst/typst · GitHub
So apparently it’s not going to be too long!
EDIT: as this is the accepted answer, I want to mention that the rest of the thread has a lot of discussion on various subsets of PDF/A. The standard that has been implemented in the PR is PDF/A-2b, but there are more restricting subsets of PDF as well.