You might manage at 18s if you stick a load more bus caps on it, but it will be pretty marginal. If I remember right the simulation only showed 1-2V of ringing with 6 of those big caps. I can probably do a special for higher voltage with different FETs, drivers and shunt amplifiers if you really want it. Should be just a small layout change for the shunts. For robot combat 80V seemed a sensible max since robot wars rules have 75V maximum.

What current is your motorbike estimated to use?