All the ToS stuff aside, Blizz has already shown multiple times that they will simply disable specific addon API features they do not want to be used anymore. Best example is probably the visual range check inside of raids and dungeons which was a thing in DBM not too long ago.
this is cool but nowhere near as cool as Castle Pineapplia
This is an amazing thing! I'm the kind of player who can read about an ability and watch several videos and still not understand mechanics, but experiencing it once or twice and I have it at once and rarely fail afterwards. Thanks to this I can spare my raid the failures as I learn and I can come fully prepared.
A more complex version of Proving Grounds would be amazing. Half the problem with pugs is that some people are brand new to each encounter while some have been doing it for months, so having basic familiarity with some mechanics reduces tension considerably.
imagine being so bad at a game that you need to do same thing over over yet still fail and install an addon to do same thing over over again...