tbh. there are forks of aros, an example is abi v0, a base for current x86 distri, which is being maintained, sort of in a separate repo, while most of work is done on abi v1, also arix and probably anubis were kind of forks. and there is sure few more, but they dont seem to gain much attention. also we provide a kind of slightly modified fork of the main repo, for stuff that doesnt belong there.
edit: and actually almost anyone contributing to aros hosts himself a fork of main repo, containing his own changes and experiments..