I think github.com/TYPO3/TYPO3 is most straight forward and looks best.
I’m against using cms as repo name.
Simple reason is that git clone github.com/TYPO3/cms would result in a cms/ folder, which makes little sense to me, all other options basically miss that same thing, you clone the repo and the folder name doesn’t contain TYPO3. Therefore I’m all in for TYPO3/TYPO3 
Further more I like the idea to fix our root composer.json name, as it is actually no longer used anywhere and that’s good to be reflected within the name.
I propose typo3/monorepo here, as it is nothing a user has to type and the name documents that.
Well, we use the github repo as submodule in production for some cases, but thanks to the renaming you outlined, github redirects will help out, so all fine, yes.