Bit of a sledgehammer there though, isn't it? Potentially introducing taint and interspersing code for every single popup seems a "heavier" solution than just adjusting the one addon that needs it.
Sure, although you obviously should have this kind of consideration any time you hook something so I don't see how this case is any better or worse than hooking anything else. I didn't say this was the best solution and it's not necessarily worse than, eg. blocking UIParents from receiving PARY_INVITE_REQUEST.