Under occupation only applies to working age people so won't apply to old dears occupying their 4 bed former family home. This seems to undermine the very nature of this initiative and a cynic (PSR) may even suggest the the Conservative party are protecting a backlash against a significant proportion of their vote as well as avoiding a more serious examination of their moral conduct.
A point not really raised is how in future we will develop the exact right number of properties to suit demand. We can't intentionally overcrowd and your penalised for under occupation. In some areas this could lead to some properties being empty.
In addition, in the North smaller properties don't raise enough additional rent through the AR system to make them viable whereas in the South the suggestion is that developing new larger properties through AR would make them completely unaffordable once the universal credit cap kicks in.
So, there you have it. If you need a big property move north, if your single move south and if your old stay put.