Ok, so KLH Threat Meter. Interesting bit of info.
I knew about the MC testing and deciding to use real players after that. Its a common failing some companies don’t learn from cough Niantic cough. Didn’t know about the mods.
That said, ultimately Vanilla was played with threat meters, debuff trackers, custom raid frames, and boss mods. There’s no reason to exclude them now because that would be less authentic.
This quote gives me confidence that Blizzard will manage the existing raid and UI mods appropriately, AND hopefully step in to stop IO and the like. Because not only did they learn that many mods are good and necessary, but they also learned that some mods are bad and not desireable.