I'm not certain that a Versys X-650 would sell in sufficient numbers for Kawasaki to warrant a build. It is not likely a simple matter of dropping the 650 engine into that frame.
Personally speaking, I would rather have the lighter weight and nimbleness of the X-300. Plus it is a parallel twin of the proven design shared over several successful lines, a bulletproof engine with guts. If that is, I ventured to off-road single track rides.
Which will likely happen shortly after I win the lottery, get that woman ( for one night only, please), am guaranteed dry weather rides every time, plus convince myself that I can still do it.
For the occasional ride on gravel that I take, my old '07 V does nicely. But that X300 is sweet.