Yeah, I like that the arbitrary nature of non-meaningful names frees us from all these drawbacks and compromises. A simple system. But outside of strictly pseudonymous places like 4chan it erodes the concept of a unique username altogether. If you're always gonna type a display name and choose from a dropdown, why even display the numbers?

Plus, now that the identifier carries no meaning, you can't type "@realdonaldtrump ..." and expect people to know who it refers to, you'd have to type "@aae0450, Donald Trump ...".