No offence but the Tri-Z was nothing special. I wouldn't say it was ahead of anything. I had one and I'd take a 250R over it anyday. As far as Yamaha making a 250 2-stroke quad, good luck.
The last thing you'd want is the Raptor suspension. The fronts are horrible and rear doesn't impress me. A YZ power valve motor in a MX frame would be awesome. They don't have a quad they could base this off of. Nothing they make would me good for this. The raptor look would be okay but you'd need a whole different chassis. I hate to say it but it would have to be a TRX style like the 400ex and the 400z are to make it one of the best.
'02 Honda 416ex - A seasoned blend of 11 herbs and spices
'04 Honda Recon - The yard machine and snow plow
'88 Honda CR250R - Another chapter in my torrid all terrain affair