Will the population of London and the South East fall as many graduates from the provinces find that they can work from home and only have to go to their London offices on occasion meaning that they'll return? Many young graduates move to London for a couple of years purely for the "London experience" however these numbers may diminish and they choose to stay in/near their home towns after graduation. Obviously people will still move up and down the country for actual studies; if anything this may actually increase rather than people attending college or Uni in their home town.
The impetus of moving for work will significantly reduce if there is a clear expectation shift in the number of days office attendance is required.
Especially as those currently in school have suddenly been thrust into a remote working situation. I'm sure part of the current 5 days 9-5 culture and 'Presenteeism' stems in part from what is drilled into you at school. Which is, increasingly, total nonsense for many jobs.