I disagree.

http://www.fxpansion.com/index.php?page=42&tab=127
http://www.toontrack.com/products.asp?item=10

That's the tip of the iceberg. MIDI percussion can sound amazing. Now, obviously, no-one expects 28GB of percussion samples. But that (the BFD collection) is an exhaustive collection of almost everything you could ever think of. A basic Percussion kit for a MIDI arranger would be a teeny, tiny fraction of that figure.

Somehow, arrangers seem to find the sample room to put in amazingly detailed piano, Rhodes, guitars, sax's, all of which chew up sample RAM, but drum and percussion kits still get the short end of the (drum)stick!

You don't need audio loops to sound unbelievably realistic any more. In fact, for many years, TBH. Add another 256MB of ROM to the roughly 1GB or so that they already have, and you would have a percussion kit that would fool anyone.

And, of course, just like better drum kits, they would be able to be used on ALL your legacy styles, not just the tiny few that come with the machine. 10% of your styles (far fewer, if we are simply talking Latin styles) doesn't really START to fulfill the need.

KITS, not loops. That is the answer.