Some things in life never change. Heart will always be the best band of all time. Tyler will always be dangerously underweight. And gem prices will always spike after a new content patch, often by 100% or more.
The best way to profit off of (relatively) short-lived price increases is to stockpile ahead of time. While it's clearly too late for that, there are still plenty of opportunities to profit off the rare gem market before demand dies down. It's not too late.
Regardless of whether or not you're a jewelcrafter, you've probably noticed that the market is going crazy. The red gems everyone wants are scarce enough to result in doubled (or even tripled) prices. And because people aren't gemming red because of the cost, more folks are buying orange, purple, and to some extent even blue, green, and yellow gems. Why? Socket bonuses are pretty attractive, and if you're expecting to have a piece of gear for only a week or two, why spend 300 gold, especially when you can get a decent boost out of a gem that costs a tenth of that?