El and Wowhead are both reporting that the Tiny Carp pets might become cageable/tradeable in Patch 5.3. Keep in mind that this was previewed on the PTR, so things are subject to change at any time and nothing is 100% set in stone yet.
If this change goes live, I think many collectors will be pretty pleased. Catching the Tiny Carp pets, while not entirely dependent on fishing skill level, does require a lot of time/patience due to the high RNG factor. When they were first released, it was pretty puzzling to me why they weren't cageable. Not everyone has the time to fish and fish and fish... and fish. And not everyone is extraordinarily lucky either.
So this change will probably make the Tiny Carps a little less rare. There is still the RNG factor, so unless many people have tons of time to fish multiple pets up, I don't expect the AH to get flooded with the carps all at once. They will start making an appearance, though, I have no doubt about that.
I must admit that while I'm for this change, I'm a little bummed that it's happening so soon. For those that spent the time and effort to obtain these pets prior to 5.3, it's a little bit of a statement to bring out a Tiny Carp. If you see a player with one, you know they either spent a hell of a lot of time fishing it up (or got very lucky). After 5.3, it will be anyone's guess how so and so obtained their little carp companion. It's not a bad thing, it's not a good thing. It's just a thing that I'm sure some do care about, though.
Ah well, times change.
We'll have to wait and see if this change to the Tiny Carps goes live in 5.3 or not.