As a straw poll from St Albans - the commuting world seems to have changed for ever. One of my family has been told she will never go back to more than 3 days a week in the London office , (2 days at home) , other "workers" consulted say much the same - ranging from 1 day a week to 2 , - or even "never" , and you can bet some of these trips will not be the 07xx to London , but at varying times during the day. So you can expect maybe a 30 to 40% peak load in future. This will have major implications on the cost base going forward.
Indeed so - it will make the railway massively
cheaper to operate, being able to just operate an all-day Saturday style service. Providing for the South East commuter peak is incredibly expensive as you have stock and staff you don't need other than for a short period from about 7-9am and 4-7pm.
Rather than the complex insertion of various peak extras and tweaking, the most you'd need would be what you tend to get on the likes of Merseyrail - a couple of key peak trains extended from 8 to 12-car in each direction (or in Thameslink's case, diagramming the 12-cars to be in the right place at the right time), and possibly not even that. Or on LNR you'd be looking at there being maybe 4 or 5 units sat on Camden Bank all day, not far more than that as do at present, and the 319s have probably turned their last wheel.
There would be a bit of a loss of income from high Anytime fares, but unlike IC routes hardly anyone pays those, peak travellers mostly use seasons, and per day a monthly or longer season is more at Super Off Peak or Off Peak price levels on most routes. So such losses would be relatively low, and I suspect the cost base reduction from not having to operate peak extras would by far outweigh that loss.