It seems Blizzard will be rewarding players who double-dipped in getting Diablo III and World of Warcraft's Mists of Pandaria expansion.
This news was unearthed in Diablo III's upcoming patch files that's due for release later this month.
If you've bought Mists of Pandaria Collector's Edition, I suggest registering your copy so you can unlock the Panda-monium, a new Feat of Strength. Aside from that, there's also going to be a new banner sigil, accent combo that comples complete with pandaren-themed illustrations and even a panda face.
There's also this code string "SpecialGiftWingsBuff_name – Collectors Edition Buff" which is attached to a pair of black demon wings. It's currently not known if this one is to hand-in-hand with the Mists of Pandaria CE, but the string highly suggests it.
Not a bad move by Blizzard, no? Hopefully, this is but a start of their cross-franchise rewards.
I'm guessing we'll hear more about this gift once the patch's officially out.