One of the most controversial parts of Mists of Pandaria is the new portion of pet training. Many players have declared it the death of serious warcraft playing when kids will join the game to "catch em all".
Blizzard and the beta testers (doesn't this sound like an awesome band name) have been giving information on how the training/battling portion of the game has occurred. To me it looks intriguing simply for the idea that it can be a gold making opportunity.
The basic idea of making gold using this system is to train pets and then sell the trained pets to other players. The more exotic or in demand pets the higher the cost. Just like with any type of supply and demand it will be whoever jumps on the trend the fastest that will bring in the most profit.
The Argent Tournament was during the Wrath of the Lich King expansion, and opened up a new type of token, the Champion Seal. If you look in your points and tokens on your character sheet the odds are that you still have some there to use. These were given for doing the dailies available in the area as well as the raid (Trial of the Crusader). It was relatively easy to finish up the dailies in a little over an hour to get between 8 and 10 per day.
Even now these pets go for between 3.5 and 4k gold a piece. And sending them over to the opposing faction auction house can add more value. When MOP introduces the pet battle system, these more exotic to find pets are going to be in demand. Especially with collectors and players who will end up with more gold to spend than they know what to do with.
MOP is also introducing a limitless amount of dailies instead of the artificial 25 daily quest limit in place now. The list of dailies from MOP is extensive for cooking and reputation grinding. But for gold making adding the Argent Tournament dailies to the list of things to do can end up bringing in a large amount of gold to the goblin coffers.
Planning will be very important on what to sell, and who to sell it for. Most players are scrambling to do things between running instances and chatting with friends. Taking a few moments to joust some friends, pick up some items and overall fly to thump some frozen Vikings might add a good amount of gold to your plans for the future.
Wowhead has an excellent guide on the Argent Tournament here. This should get you started with grinding out some seals towards pet dominance.