I agree that this change is crap-tacular. Changing part of the game's history that's been around for 30+ years, purely for the sake of having a change, is a very bad idea.
That said, the fun from this will be trying to tie the new status of the planes back in to the old status. For example: suppose the reason that there are no more humanoid demons in the Abyss is because of the Savage Tide? After Demogorgon was defeated, the obyriths made a successful comeback, destroying many of the tanar'ri and routing the others. The devils, for their part, are now capitalizing on this. The Infernal Ministry quickly orders all erinyes to be biomantically modified, and are now called "succubi" - all the better to earn them additional summonings to the Material Plane.
This sort of retconning can be very enjoyable.
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