Don’t hope for any performance or efficiency increase going higher in voltage. For Esk8 there is not much gain going higher in voltage…
What Mario said 
The fact though that your BMS will fit in the space of the original Onewheel BMS is huge (assuming it will fit in the thickness dimension; the Onewheel BMS is 157x37mm). This will allow Onewheelers to replace the whole ESC + BMS combo bascially in-place, without having to come up with some different placement.
That said, I’m looking at ENNOID-BMS-SS-LITE after Mario mentioned it. Supporting up to 24S eventually 
And I don’t think it’s unreasonable for a narrow version to happen. If there’s enough onewheelers out there… (the thread: ENNOID XLITE & VESC)