Probably the fever dream of many Oligarchs. :P But in all seriousness:
I think the term "microgrid" started out because that's exactly what they were... small grids in places like islands or rural areas.
We learned a lot about how to make a sustainable grid in this contexts, and so the term sticks a bit, even as we start talking about macro-scale microgrids, or just decentralized generation. Especially because the "micro" element of these new grids plays a much larger role.
Also... regulations, protocols and standards are a form of centralization, which will all play a large role in these "smart" grids.
From what I can recall of the Tesla/Edison disagreement, Edison was building microgrids for wealthy individuals. Tesla had solutions that worked over larger distances, and Westinghouse enabled him to do it (starting with the hydro power plant at Niagara Falls)
Except, my surface level (pun intended) understanding of this, is that it's actually not that simple. AC may have been easier to deal with at high voltages (and thus long distances) at one point, but due to the skin effect and RMS power not determining the safe tolerances for transmission lines (I think this is true), there are some issues with this approach.
Nowadays, it's possible to build safe HVDC systems, I think partially due to the existence of HVDC breakers.
That said, you lose a channel of communication assuming your power is DC, and that signal is used in AC to help shape the generation / switching / etc. We could always try superimposing signals on DC power lines, but I digress.
In this context microgrids implys many small grids, and decentralized implies no centralized organization of energy transmission.
You can have a decentralized macro grid much like the internet is a decentralized network. You can have a centralized micro-grid which would be many small grids using a single authority.
