This seems plausible.
One thing to keep in mind, is that any legit leak, likely comes from 2nd hand information. Employees that are close enough to the project to know all of this, are not likely to risk their career to share it early. However, they may tell their friends or family. And some of those people, may decide to post it. So it would be safe to assume that some of these things may not be word for word.
core Horde faction, led by Sylvanas, and a core Alliance faction, led by Tyrande
This does make sense, but not with them leading the current horde / alliance. Instead, they would be leading what they would consider to be the TRUE horde / alliance. Basically those that did not accept peace and continue to fight.
Level Squish - Us getting weaker
I actually like this, and it may be the only way I could somewhat get on board with a level squish. Some of us just need a reason. I understand the REAL reason will be for the systems side, but having it make sense that I am no longer as strong (or the world around me is far more dangerous) is a good plan for many of us that just want something to explain it. I can get on board with that.
A lot of the other things all could be educated guesses, or legit. Things like them giving back class abilities are logical conclusions based on where we are and their past statements. Reworking old content again makes sense if they are going to use it again at max level. Cheap way to produce "new" content that people also have attachment to. Tinker are the obvious next class, and something that many are interested in.
All in all, sounds like it could be legit. Will know in a couple weeks.