I think his point is that the generators now have to be sized based on Art. 220. Gone are the days that you can install on gen on probable use. Load shedding does give you more options and we have had to do so on several of them.I think this is a single dwelling we are talking about.
I have never had a problem with installing a 40kw or even a 20kw generator on a 400 amp service for a dwelling, I could see a problem if it was all electric and no gas, but around here its almost all gas heat and cooking.
I did have a 15Kw Generac balk at two AC units trying to fire up at the same time of transfer on a 200 amp service, even with the built in time delays in the thermostat they would still both try to fire up at the same time, a couple of time delays set to fire up the 5 ton first then the 3 ton work great, but when we did 10 Kw ones we would always do load shedding by installing a separate 100 amp panel and just placing the needed loads in it and no AC's.
I would say if you use a 20kW on a 400 amp service and there are multiple AC units, just have time delays installed on the unit so they each fire up one minute apart.