Saturation point? No, not quite....
Given another runway in the LTMA and STARS (and SIDS) that keep aircraft low (and the extra controlled airspace to support those ops)... and agreement from operators to enter the LONDON FIR below FL200 from continental EUR.... etc etc.
That said...
Chances of more concrete?
More CAS?
Agreement to use low level STARS/SIDS?
More ATCOs..... ????
So, it could be done. Practically, it will not be.
rgds BEX