Few Ideas, please read : )
I have a few ideas that I think would be great changes to the username system. To start off I believe the "4 letter" name rule is far outdated I don't see an issue with 3 letter names being allowed, some user already have 3 letter names (I.E. XqC, ABE,Pat,Red) so it's 100% doable. Another change that I think would be great is to allow more characters/symbols in names, such as ( ' - ~ / \ | ) ETC. Including symbols diacritics (e.g. ú, ÿ, ç, å, ē) should also be allowed in usernames, they're already used in other games/sites such as Blizzard. Lastly I think the name recycle time is to long, should be reduced to if a name is inactive for 3-6months then it becomes open. I also think that even if the account is a partner or affiliate if they are no longer using the account the name should be open. It's obvious Twitch is growing much larger and fast, unique usernames is a great way to distinguish our selfs from other streamers/viewers and with the growing population on Twitch alot of names are no longer avalible. Just a few idea's I had please share thought's below!
p.s. if a staff see's this and whats to give me the name "sev" feel free too : ) <3

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PonPonTheBonBon commented
Diacritics should at least be allowed for display name instead of username. This ensures that everyone can type the username at least.