I seem to remember in the 1950's, the "Jazz services" - the Great Eastern suburban services out of Liverpool St, were run very efficiently with steam power, with fast turn-rounds achieved by the incoming engine moving to the head of an outgoing service on an adjacent platform as soon as its stock had been released. But then, as has been said, there was the infrastructure to allow such slick operation.
And, I suppose now a return to the "push-pull" or auto train design would solve the problem of lack of turn-round facilities at termini.
And there were tales in the 1960s of steam engines being substituted at the last minute for failed diesel locos [often much to the crew's chagrin, as they were looking-forward to a clean, comfortable ride], and achieving creditable timings, nevertheless.
But what would be the point now? Since the run-down of the collieries, there would not be an easily-mined supply of good quality steam coal now available, to say nothing of the distribution of that coal and watering-facilities, water troughs and columns, etc. When steam specials run now, the often have to be scheduled stops of up to 25 minutes in a loop and at a convenient point where a bowser can be adjacent.
I suppose it could be a good use for all those locos being kept in warm storage in Box tunnel, though.