Shortage of power is a good enough reason.
Not very likely, as a few random houses at a time won't be anywhere near enough. In any case, if the problem is a shortage of generating capacity, disconnecting houses won't be much use: they are not a significant part of the peak demand. That comes mostly from industry, commerce and transport. People at work don't normally use a lot of power at home.
There is a good reason why stored systems are call off-peak.
In the event that we do run out of generating capacity and we can't bring mothballed plants back on line, the first step would be load shedding on a voluntary basis, as already agreed with a number of large users. That ought to be enough to deal with any predicted shortfall.
However, if it is not, the next stage would be rationing electricity to major users. Allowing fewer trains, for example, then, possibly reduced working hours, as we saw with the three day week in the 1970s, although probably nowhere near as drastic.
Disconnecting domestic users would only be needed if capacity were very severely restricted, as it was during the miners' strike by lack of coal. In that case, it would be done by disconnecting whole areas at the sub-stations, so it wouldn't matter whether you had a smart meter or not.
The only reason to be able to disconnect remotely is that it is a lot cheaper than sending somebody out to pull the company fuses or, in extreme cases, dig up the road and cut the cable, for persistent non-payers.
Colin Bignell