Disclaimer: I don't know anything about programming, but I'm hoping this wouldn't be a nightmare to code.

I would love a second price line when setting pets up for sale to add a diamond price. That way I can sell my pet for either gold or diamonds. You can fill in both fields if you're wiling to take either currency and If one of the two options is left blank, it means the seller doesn't want to accept that currency.

Examples:
I put 200,000 gold in the gold price box.
I leave a 0 in the diamond price box.
This means that I'll only accept gold for this pet.

or

I leave a 0 in the gold price box.
I put 100 in the diamonds price box.
This means that I'll only accept diamonds for this pet.

or

I put 200,000 in the gold price box.
I put 100 in the diamonds price box.
This means that I'll accept either 200,000 gold or 100 diamonds for this pet.

It would probably end up being used as a currency trading tool, no doubt, and players would still put up randomly bred pets for diamonds and complain when no one buys them. And the releasers of sylestia probably wouldn't want to spend diamonds to clear out all the cheap diamond-only pets and release them. *shrug* But anyway, that's the gist of my idea.

I personally would love this, as it would make it so much easier to sell pets for diamonds.

It would also be great for cases where you don't care about whether you get diamonds or gold.