It's been claimed to have been done already (asian/jardini). Here's the post on arofanatics:
http://www.arofanatics.com/forums/showthread.php?t=21364&highlight=pearl+hybrid
I think the pics have been removed, but the poster's avatar (robo) is the claimed hybrid.
I think an asian/jardini hybrid is possible, but the problem would be that the offspring probably wouldn't reproduce. I think this is the same as a mule. The male ass with the female horse produces the mule, but the mule cannot reproduce.
Another interesting side note is that the usfws would view a cross between a formosus and a jardini as a formosus hybrid, and any varient or hybrid of the formosus species is still illegal for import into the united states.
