I dunno, I think I could see a lot of this stuff being very plausible.
Why? 'cause I highly doubt we're going to be tackling the Legion head-on next expansion. Plus Wrathion would be the type to abuse timestreams and bring people like Illidan over to help fight the Legion once they actually arrive. And it gives us an expansion to basically redirect our focus towards the Burning Legion by looking into alternate realities...
Plus there's evidence that scalable raids/dungeons is going to be very real. The devs mentioned sometime in August that the scaling technology had basically been finished, and sometime last week someone discovered a glitch/bug while in Stratholme where he was suddenly scaled down stats-wise (at level 90) to iLvl 43 gear and was easily destroyed by a bunch of level 40ish mobs.
As for the Infinite stuff in general, we already know from the Timeless Isle questline that there is indeed a traitor amongst 'em... Mal'Ganis, though? Seems a bit far-fetched, but it is plausible since in WotLK it was revealed that he's alive and all we did was force him to flee to some other realm or whatever.
With Illidan's "revival" of sorts, and bringing him back to our timeline... beyond Wrathion being the guy who'll stop at nothing to defeat the Legion and protect the planet he loves so much (and presumably the people, even though he uses us as weapons and tools for his plans to beat away the Legion), I can actually see it being plausible as well. 'cause Metzen mentioned back in 2010's Blizzcon that he'd like to bring Illidan back since he's a sucker for a good redemption story. In 2011's Blizzcon lore Q&A, he said that they would work on figuring out a way to bring Illidan back. So going back in time would make sense to retrieve him, though I really don't think it would work to retrieve him from the Black Temple... it'd probably need to be earlier, like maybe even before he absorbs the Skull of Gul'dan. 'cause in Burning Crusade he was pretty much mad, since he went to ridiculous lengths to try and stop the Legion, and for some reason became our enemy rather than working with us to stop the Legion.
The alternate leveling path for 1-90 would be huge and IMO great for those who don't want to go through the fairly long leveling process otherwise. And it seems like it would be something Blizzard would do to help people get up to the expansion faster.
Overall, most of the ideas Murozond presented sound like they could make for good expansion material and most of the stuff sounds very plausible. And it somewhat fits in with the supposed leaks from that Chinese site which also talks about an expansion focused more on tackling the Infinite Dragonflight and investigating at least one alternate timeline.
Plus having alternate timelines could set the stage for a Warcraft 4 RTS, which could simply continue off of a different timeline where there might not have been so many heroes willingly ready to tackle the world's threats.
Also, alternate timelines are pretty much already existent. Rhonin, Krasus, and Broxigar going back in time during the War of the Ancients is a good example of this, 'cause that happened in a book trilogy and yet in the War of the Ancients instance in Cataclysm they were never seen there; Blizzard probably did that on purpose for some reason or another. And the Timeless Isle quest chain shows an alternate timeline where Garrosh is killed. And End Time shows an alternate timeline where things go to hell if Deathwing isn't stopped. So it's not like these alternate timelines aren't visitable, since they clearly are, and they can alter future outcomes which is why the Infinite Dragonflight has been messing with the timelines so much. Plus with the Bronze Dragonflight unable to really do much now, that allows the Infinites to potentially screw with the timelines quite a bit and make several alternate realities.
So if you simply made all of that up, kudos for creativity. If that's actually a leak, then I can't wait for them to reveal it at Blizzcon.
Less than two weeks... >.<