Re: I think it *will* be a ghastly mess
Netflix have both far more users and far more - and unique - data to send.
If we did assume a need to distribute spot price to all meters in the country, there is such a thing as "multicasting", where you send the same packet to all subscribers.
Cellular networks also have a lot of low-level stuff that goes out to every single mobile telephony device, which could be used instead of IP-over-GPRS or similar.
However, I have yet to see any argument that instantaneous spot price is either necessary or desirable at the meter, as opposed to simple banding and shedding command signals.
Those are commonly done with low-frequency signalling on the actual mains supply. (See France)