I wouldn't want a Ninja 250 as an offroad bike, they are quick top end wise, yes, but they don't have nearly the torque and low end grunt you'd need for a GOOD trail or rough country bike. Too high, too top heavy, too heavy period.
A BR 250 swingarm most likely wouldn't fit, ever saw one? And yes, they are all shaft drive, the only 250s that were chains were the tingers, and 125s are hard tails.
How I see it, the only way to make it handle decently either on/off road, would be to lower it, lengthen the front rake, and probably widen the axle, and that ruins it's offroad capabilities. And it'd probably still sit way too high, and with all that much weight that far forward, you'd have to sit on the grab bar to turn with any speed, I don't think leaning like you normally do would cut it.
I'd still own it if it was VERY affordable, just to dabble with it and see if it could be made into something better, but buying it to use hard as is, no way.
This is my trike. There are many like it but this one is mine. My trike is my best friend, and it is my life. I must master it as I must master myself. My trike without me is useless. Without my trike, I am useless. I must ride my trike true. My trike and I know that what counts is not the amount of miles we ride, but the time we ride together. My trike is human in it's own ways, therefore I will learn it as my brother. I will learn it's weaknesses, it's strengths, it's parts, and it's soul.