I want to rename my fork of this repo to tangled or something, and my fork of tangled.sh/site means that I now have a repo called site that isn't actually my own site. :P
(Of course, a separate thing could be just the ability to change the fork name upon creation, but this is also good.)
As a temporary solution: you could git clone the repo, delete it from your profile, create a new repo with the name you want, add the remote, and push. It's not the best but it's a decent enough stopgap till they add this functionality.