With 3/4 rwys at LHR anything becomes possible.
Not ACI, and if EMA is viable, so may BHX, NWI and CWL be as well. Would expect either DSA or HUY but not both.
All the above, and others, are crying out for an LHR link, but not convinced that BA would neccessarily be on
all of these routes.
AFAIK, they don't have the aircraft suitable for the thinnest routes.
Could see other carriers on the thinner routes (BM or BE perhaps?), perhaps in collaboration with BA and/or VS, (through ticketing and baggage checked through to final destination, etc.).
Also suspect that commuter flights will come into their own with increasing congestion on the roads and another 10 years of above-inflation rail ticket hikes. Feeding longhaul as well makes more of these viable.
As for BA flights, or VS for that matter, think
adfly's list (see below) is about right.
However none of this will happen without the elimination of the delays, congestion and the artificial market in slots at LHR, and that means 1-2 more rwys and new terminal capacity. Under those circumstances could also imagine a U2 presence at LHR for some of their more busines-orientated routes!