I try to limit the amount of posts about gold making tricks that contain speculation or haven't been verified by myself, so excuse me. But if you do it right and really need some super fast gold, there's lots of potential.
Drink a swiftness potion. Drink two.
The new "BOE" pet is a curious thing, but it's hard to predict what kind of impact it will have on the economy. After all, no such thing has been available before. It's like Blizzard is selling gold in their store!
There's quite a few things that may happen and here's my thoughts on them.
The first person to sell these will make the most gold off the more impatient pet collectors and clueless people in general. A person advertising this pet in the trade chat may even get 10-20k offers for the pet. Perhaps more as over half of the players don't even know where the pet comes from or that there even is such a pet. Then again I'm the wrong person to guess the amounts that pet collectors would be ready to pay for new, useless, fluffy.. cute.. but still useless things.
However, since anyone can buy it from the pet store and it's a one time use pet, at least half will sell it instead. So it wouldn't surprise me to see 10 of such pets available at a time in the Auction House, where each seller attempts to undercut the other. This makes trade chat a bit less useful when more start to sell the pet, but at least there won't be auction house cuts and deposit fees.
There's always those that would like to monopolize it, so it's possible the prices could have 5 numbers for quite a while if someone attempts it.
Blizzard Store vs. Gold Sellers vs. Gold Making
After checking the current prices for gold, the average amount you could obtain from a gold seller with $10 is 5000g on a larger EU realm. So purchasing the gold from the pet store instead may very well be more profitable, at least for a while. Who knows, maybe there will be 100 Cubs for sale on a bigger realm some day, for as little as 1000g each.
So, if you need gold and have $10 to spare, it could be a quick way to earn who knows how much, as long as you make sure you do it instantly when it's available in the pet store. Though I didn't see a mention of a release date so it may be hard to be the very first.
If you weren't fast enough, there's still more gold to be made by selling something else instead. Pick 10 or 15 methods from this blog, attempt them and you should have the same 20k in a day or two. c: