This is why I've spent so much time working on and understanding the OpenMLS library. It's a really solid open source implementation of the MLS spec that I think most client devs will use to implement this NIP. 

Of course, once this NIP gets some feedback and settles down I'll start work on implementing it myself and adding the necessary abstractions to NDK (and other nostr libraries) to make it easy on client devs.

That said, it's quite different to the way that people think about DMs so far. Each client keeps it's own chat transcript and has it's own set of keys and state so it's less "syncable" than something like NIP-04 or NIP-17 DMs.