Not all my thoughts relevant to this topic but anyway...
You can't bash 273 really hard, it is 20.5kg plus tyre & rim and you might end up with 23kg at least. It can work as cross-country type of bike, but certainly not as motocross. It goes as a tank but you will feel heaviness in rear suspension much more than 205 hub (16kg).
The smaller rim the more dynamic ebike gets from a standstill (of course less max speed). I'm sure you know it as an engineer, but I'm just saying that there is the difference between 17'' and 19''.
Considering qs 205. Starting 190Nm in 17'' rim is a lot torque. You can push through qs 205 hub up to 150A in peaks and an even little bit more if will some cooling method applied. Losses start to increase even more but who does not want few additional Nm.
I've tried few days to ride 273 V2 - old version (with 40mm magnets, 16'' moto alum cast rim) with 130A constant and 250 phase. It was not quicker/more dynamic than qs 205 with the same settings ie 130A / 250A. Just saying that if you get 273 it will need more amps justify additional weight. The good side is big sheer masss hub never got hot, but we got FF and hub sings already. Nevertheless, I adore 273 looks.
I've looked regarding 273 hub and I see in QS page they indeed do cross spoking.
Somehow mostly I see only radial spoking on 273.
I have seen many conversions and people are going following way:
first bike - basic hub 250w/500w (gets no fun in few days...)
next - MXUS (not enough starting torque and/or heating issues...), now it is solved with cooling.
next - QS 205 (what if I get more power)
next - qs 273 (omg that's fast and heavy, if it's in ebicycle frame)
next - midrive (engineering skills, top line)
I'm in qs 205 phase. Going to order qs 205 soon. I hope I'll be at least five years. I was planning middrive but sold PMS120 (Brammmo motorcycle motor) and other parts. There is nothing more bullet proof than a hub, it's like two cents, eh.. maybe little bit heavier.