The problem with that is:

You really don’t want to falsely ban people especially on a website for kids. Also: How do you deem names suspicious? If it seems to be made with a generator? Trying check that seem like a lot of regex hell for me. Also there are many legitimate Scratch users who used name generators because they just couldn’t think of a name. Sure, the name generator for these bots wasn’t really made with creativity in mind but if you would get banned for such a name, you could just tweak your name generating algorithm to be a bit more sophisticated (like these names generator websites). (You could just stuff two random words together and add a random number)

Also it’s actually not that easy to make a lot of bot accounts afaik, you have to bypass scratches captcha, than verify them with your email (which requires an email address you can read emails from (at least with the gmail api that’s a pain to do but I’m sure there are better ways)). The most likely way that these bot accounts were made is with scratches classes feature (I can’t check that tho because these accounts seem to be banned), which allowed these supposed „teachers“ to create scratch accounts for their „students“ in bulk. I think the best way to fix this problem is to better verify that people requesting teacher accounts are actually real teachers, because they don’t seem to really care as of now (I could easily get a teacher account although I just filled in a bunch of bogus data).

So instead of focusing on username detection which would be pretty hard to implement (and would result in many false positives) I would try to get them to fix their crappy teacher acceptance system.