There WAS a big community outcry when Ion said "flight is not going to return".
Whether the outrage itself was accompanied by people ragequitting the game or not is completely besides the point.
Fact is: the outcry was enough for them to change their mind and offer Pathfinder as a compromise, which largely seems to be an accepted solution by both sides.
So for Blizzard this means: case closed.
I don't believe the DEVs always wait until them magical sub numbers are affected. I doubt DEVs are as fixated on these as some of the playerbase is. That simply wouldn't be good business because a lot of people won't re-sub once they move on. So it is in their best interest to react BEFORE it comes to mass quits, after all, it is their goal to keep the game alive an healthy. Doesn't mean they don't make mistakes, doesn't mean they might react to slowly at times (Blizzard is a big entity, not some 3 guy indie studio). They are human, after all.