One of the features of the late Google+ I continue to find intriguing was that account identities were
not based on any semantic terms, but rather on a nineteen- or twenty-digit numeric string, apparently randomly assigned and not in any determinable sequential order. Descriptive account handles were effectively aliases assigned to these, and yes, multiple accounts could share the same alias, as both my primary "Edward Morbius" and secondary "The Real Slim Shady" accounts demonstrated.[1]
Eventually, Google hit on the idea of offering "vanity URLs" to members, with the catch that you had to provide a phone number in order to get one. I demurred on that basis, but discovered when the service was discontinued that one side-effect was that posts referenced by those vanity URLs weren't archived by the Internet Archive's Wayback Machine ... and that there was no viable way of mapping from the vanity name to the canonical numerical ID. People who'd elected to use those IDs were doubly screwed in the cancellation as their content couldn't be archived, even if they otherwise wanted it to be.
Random numeric identifiers were also a characteristic of MCIMail back in the day, if memory serves. Vint Cerf worked for MCI before moving to Google, and I wonder whether or not he had any influence in either system's account identifier policies.
This whole story-arch of Twitter's enmuskification would have been mooted had a similar architectural decision been made a decade and a half ago. I'd also strongly recommend any future account-based systems consider this model as well.
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Notes:
1. I created TRSS after getting locked out of my principle account, in a fit of pique. Given that I was already pseudonymous, why not emphasize the point, particularly when trying to reconnect. The fact that the new account pretty rapidly reestablished relations with my principle prior contacts was ... interesting. How much of that was algorithmic, how much social function, and what that has to say about both impersonation and reestablishing identity strikes me as interesting.