For me, the problem will be with stopping motion instead of hand shaking
Precisely.
Even if OIS or dual IS affords you 3+ stops, realistically you'd probably still want to be 1/400s and faster for subject motion.
But having done some quick calculations, it's really only 1+ stop or so behind eg. a D7200/D500 with 200-500/5.6 lens at 800mm equiv, although the IQ of the D500 is yet to be verified. So for the weight and bulk saving its not too bad actually.
Cost and focus performance of the relative systems is a different issue though. We also don't know how good the 100-400 is wide open @400mm although I presume it should be pretty good.