How about nano controllers that each have their own source of power and share a common battery bank (s) and are controlled by a common controller. We are sort of going that way with follow me then bully wimpy modes and Steca doing a dual MPPT controller in one box with one brain. The ground work is here. I can see nano controllers coming maybe like Ralph Heisey's new controller with separate brain/ data logger and slave charge controller. One brain/ data logger and 4 or 6 or whatever nano charge controllers each with own source of power. Not that far from panel mount MPPT nano controllers for grid tie.
td