I'm still toying with the idea of a kx100, but with heavy modifications.
There are 3 problems with the KX100.
1) wheels are not full size
2) wheelbase is way too short
3) front rake is way too lax. It feels like riding a chopper.
Things I love about the KX100:
1) kips valve, so it has more torque
2) seat height is perfect
3) 150 lbs dry (that's only 6 lbs more than my trials bike)
4) really good parts - USD forks, disc brakes front and rear, water-cooled
5) 10.8" of travel - just enough for trail riding, but not so much that it makes it tall
6) low seat height
So here's what I'm thinking...
1) find a cheap kx100
2) add a 10-16 oz fww
3) re-lace the wheels to 21/18 wheels (possibly a trials tubeless rim in the rear?
4) rear trials tire
5) stretch the rear swingarm about 2" to fit the 18" wheel and lengthen the wheelbase
6) this is the scary part - extend the front of the frame and change the head tube angle to be steeper. I'm thinking a 2-3" stretch will be just about right.
After all that, I should have a super lightweight bike that has a low seat height, good suspension, great motor, and fun to ride. That's my thinking anyway...