One guess in London will be young middle class people living in delapidated council houses? It sounds stupid now but what else is cheap in the centre? I was living in one a couple of years ago and they're ironically often more spacious than new=builds. Known several friends do the same. Also, will the centre shift southeast? I guess the relevant question is whether and which businesses follow the pricy housing shift. Like I can't see finance moving from old street/c wharf, but you find tech up towards Kings Cross and at the Eastern side of Old street? And tech is basically the new finance. But those business moves seem a lot smaller than the amount that young prof.s seem to shift around in a couple of decades.

Edit: Another thought, this is a trend driven partly by destruction of council house stock, oligarchic money laundering, etc etc which has created extremely high prices in the centre. If that bubble pops and Brexit murders UK economy leading to a long period of price reduction, maybe young middle class people will go back to living in Kensington fancy houses/flats.