Well the big news is aptly summed up in the image above. Yes, it's the Onyxia mount (though not actually the Broodmother herself). A picture really does say a thousand words, doesn't it? However that's not all he's found by datamining. There are yet more mounts, including a Spectral Tiger cub! I suspect this little cub may well be from a future TCG expansion. After all, where did this little guy's parent come from? Ditto the rather awesome Tuskarr kite.
On top of that there are some regular mounts in the form of a Little White Stallion and yet another dino-centric mount, this time a Little Ivory Raptor. Boubouille also found the Onyxia Whelping, which is the pet everyone who logs in during November will recieve (think the Blizzard Bear). Ain't it a cutie?
However the oddest thing he uncovered was a collection of Mohawk themed spells. These relate to the now memorable TV advert in which Mr. T creates his own class, the infamous Night Elf Mohawk. From the spell descriptions, I can't help thinking this is not some hint towards a new class in the next expansion but, rather, will be some kind of NPC or quest-related summonable pet. Either way, it sounds awesome.