You would then not be allowed to call it GNU Parallel due to possible trademark confusion. This also why we have names like CentOS (not RedHat Free) and IceCat (not Firefox Free).
There was a court case in Germany about this (for some CMS tool - IIRC) where a forker used a similar name. The verdict was pretty clear: Forking was OK (copyright law - permission by GPL), but keeping the name was not (trademark law - no permission by GPL).
Good Q! I don't know, but I also feel like that could be a bit dirty, without having other reasons to fork. I might not want to encourage or support that.
There are some (non-fork) projects that provide the same functionality, with the stated motivation being in part because of the citation thing.
Nothing homebrew can do about it, of course, but this illustrates one of the implications of parallel doing something unexpected; package managers have to field the complaints.
I’ll look again later today. I tried to find one I saw earlier quickly when I replied above, but I didn’t see it. I think it was also called “parallel” and it mentioned the citation being a factor.