Honestly, it's surprising to me that Blizzard hasn't brought back more ways to get the TCG pets/mounts/miscellaneous items. Sure, they pop up in the BMAH occasionally, but unless you've got huge sums of gold lying around, you're probably not going to get them, especially if someone dumps the gold cap immediately and locks down the auction. I get that they're valuable because they're so rare, but Blizzard isn't really making any money off of them anymore, barring people that buy WoW Tokens to get enough gold to buy one.
Obviously it would make the few people who are still hoarding TCG codes buttmad, but dropping those items in the store would be instant money. You'd probably see a lot of Swift Spectral Tigers running around for a while, but then the novelty would wear off and people would go back to their normal mounts.
Or they can give away more of them for some free goodwill, like they did with the Bananas pet a while back. Again, the people that paid out the ass will bitch about it, but I'll bet the majority are just happy to get free stuff. In the end, it's just pixels in a video game, and if you spent hundreds of dollars just to buy a single mount you probably haven't used in a decade, that's on you.