How fine grained do you want this to be? The point of cost allocation is that grid upgrades and additional capacity overall benefit everyone - basically that electricity exists as a reliable and relatively cheap commodity to all comers. Especially industrial ones. It more or less enables the modern world.

If you're the last house on your block to upgrade your home service to 200A in order to charge an EV, should you be cost allocated 100% of the distribution transformer upgrade that happened to be needed to service you? After all your neighbors were doing just fine until you wanted more capacity.

How about the new subdivision of 200 homes that requires a regional transmission line upgrade? Does that developer (and thus new - typically younger - homeowners) need to pay for the entire upgrade or should that be split over all the ratepayers? Utilities don't tend to upgrade lines to meet exact current demand - that upgrade is going to be spec'ed to be good for decades of additional growth so the next subdivision next door is going to be effectively getting a free ride.

I agree cost allocation needs to be fair. Part of that is the "last comer" is not the one to bear all the costs of needed upgrades. Otherwise things like rapid EV chargers in office parking lots would never get built.

Cost of generation kind of takes care of itself in a sane market. That's just called a power bill. If it's being priced in a way where one user subsidizes another that simply needs to be fixed. Typically those "subsidies" are going in the other direction though as constant 24x7x365 usage is much cheaper to service than rare correlated demand spikes residential users give you.

The transmission grid is a much harder thing to cost allocate fairly.