The only thing I really have to say about AO3's latest contretemps is:
I told you so~When a platform is so fucked up that the only way to make it run is to take out the navigation, then it's time to think real hard about who's been driving development.
(Dropping in from link-hopping)
The first time, I eventually got a nice reply saying "Oops, we'll sort that" and the names became Name(Fandom One) and Name(Fandom Two).
The second time I got a snotty reply about how they could only go on what names were there, and nothing could be done about it. When I grumbled about this on Twitter, I got a long lecture from a total stranger (friend of a friend) about how hard it was to be a tag-wrangler and how I had no right to complain because I wasn't even a user. (I'm not registered. And given it takes six months to sign up...)
So, the option exists, but...