Maillist discussion is available at: https://mailarchive.ietf.org/arch/browse/mls/
The submitted versions are available at: https://datatracker.ietf.org/doc/draft-muffett-end-to-end-secure-messaging/
A work-in-progress feature comparison of popular messenger software against this standard, is at: https://docs.google.com/spreadsheets/d/1UjZhZjq-Afg0ZPrEUcvmVRYDDIrPH77PVyEJHRUZyqQ/edit?usp=sharing
The current unsubmitted draft text can be found here; please note that: HTML versions may be out-of-date with respect to main copy, due to caching.