I've been looking across internet at all the places FR fans gather and I haven't seen them this pissed off since the Spellplague.
The worry is they are retconning Drow Lore big time, making all none Menzo cities disappear and the Dark Seldarine as well.
I'm not amoung them as I think this impression has more to do with careless PR folks who ****ed up and misunderstand the fan base, in their hyper focused hype the likely miscommunicated the Udadrow outside of Menzo. I've seem poorly done PR mislead folks heavily before. The Sundering Series of novels was supposed to be about the Sundering and outside of bit and pieces and The Reaver the series was really about the War with the Shadovar. You see this with trailers as well, hated the Star Trek Beyond trailer, it made the movie look awful, yet adored the movie.
Still if the rage keeps building this could get very bad and spill over into a problem for AFR. FR fans don't having huge parts of their setting deleted, again and so will lash out hard.
Again I don't this is happening, but the PR makes it look that way.