I looked up the requirements on wowhead and it said required engineering 500. You actually have to have engineering 600 for the pattern to drop, so I ended up leveling my alts engineering skill and then it dropped for me. Few level 90s and a level 86 all got the pattern.
For me I spent about an hour to get mine off the mobs in valley of the four winds ( this is after I spent a hours getting my legendary cloak on the timeless isle and having no luck there). Then wen we went seige of orgrimmar for our guild raid 3 of them dropped in a space of 1 trash pack
I'm currently making two of these, One I will use, the other I will probably just give to someone, I don't think I could even be bothered to go through the hassle of trying to sell it when it comes available, Because there are going to be tons of these, i think on my server there is going to be at least 25 hit the AH, and then everyone will want a return fast, and the price is going to plummet so fast, The best price for this mount is going to be after a couple months I think, when there isn't as many people making it.