The post you linked is not from one of the lead devs, and from what I hear DMs are pretty far down the roadmap but I don't have a reference on-hand.
Considering the entire protocol design I don't think DMs will be that easy to implement. They'd need some form of asymmetric key encryption scheme for personal data servers and messages would then need to be read directly from the relevant personal data servers as the app view servers would not have the necessary user private keys to decrypt stuff. Will be interesting to see how they solve it for sure. But as you point out, probably far down the road map.
That’s about right. It only gets really daunting if we decide to do e2ee, which we’d really like to do but have to decide if we can afford to spend that kind of time. Might be smarter to just make signal username sharing btwn users easier in the short term.