What would be even better would be if power-producers and distributors (or, more likely, aggregating intermediaries) made available some APIs that provide real-time data on pricing, sources of power and a degree of "peek a little way into the future" prediction. Then we could build/install devices that take advantage of that data. e.g. A fridge could heuristically trade off power price, next-hour likely pricing, source (maybe I prefer green energy or energy generated 'close by', and am willing to pay some premium; maybe I don't care and just want cheap), internal temperature and local time-of-day usage patterns affecting temperature management. (I chose 'fridge' as the example because its energy consumption can be time-shifted, but only to some degree. Eventually it is going to want to switch on regardless of energy supply conditions.)

On the flipside, appliances (water heating, fridges, cold-rooms, space-heaters,e tc.) should be encouraged to talk back to the suppliers APIs to indicate likely near-future demand, current constraints and demands and so on, so informing the 'grid' with demand data at micro-scale.

I guess this is something like what people might mean when they speak of making the grid 'more intelligent'...

Ironically this is one problem which is incredibly well suited to a market based solution, but the lobby groups which typically advocated for "let the market decide" (e.g. heritage/CATO/Americans for prosperity) took a lot of their money from fossil fuel companies. While "let the market decide" was a workable message when fossil fuels were cheaper than renewables, it no longer works for them so they no longer advocate for it, so it's not an idea that is pushed very hard.

Exactly!