That doesn't fix the info leak though, you're still leaking approximately when the account was created. Knowing whether an account was created in 2003 or 2023 is a pretty significant amount of information even if you just know that it was created some time between June 2003 and August 2003.
I mean it's certainly an improvement over telling everyone the millisecond the account was created, but if account creation times are to be considered non-public info, I would probably just not include any version of it in public facing user IDs. And if you do consider approximate account creation times to be public (such as HN, where anyone can see that my account was created July 1, 2015), then adding some fuzz to the timestamp seems to be a good way to avoid certain cryptographic issues.
With massive amount of data this would negate the performance advantage completely. Related data is no longer stored close to each other, every time-sequential access is a cache miss ...
