This might be more effort than it’s worth… It would catch reserved_username1 but it probably wouldn’t catch official_reserved_username, right? this is the type of thing that a motivated person would always find a way around.
We have a regex setting for blocked/censored words, and that seems like a reasonable way to enhance reserved usernames (which only has the wildcard)… but does this problem come up often enough to justify prioritizing that? I don’t think it’s a complaint we’ve had often.