@nprofile1q... Hey Scott! I'm so glad you're tackling this issue. I have lots of trouble with DMs on Mastodon. I think you're addressing, these, but here goes:
The biggest one is how easily they're confused with regular messages. I routinely mess this up, and make private messages public, or vice versa.
The next is how hard it is to visualize threads - especially in the existing notification section. I often lose my place in complex discussions