Its hard to say how BT choose to enable cabinets at a later date, though looking at the rollouts so far in my local area and elsewhere there do seem to be some common themes.
1) Residential is the main area for enablement
2) Town Centre cabs- not seen any enabled
3) Industrial estates do not get enabled
Ive seen new build esates have their cabs be planned for a later phase, will likely see all resdential cabs that are profitable enabled.
All cabs are above ground, generally to find a cab they are on the main roads, so wont be deep in a estate for instance.