The connection I made(!) was to domestic and I understand that the general preference is going to be to use the low numbered gates in the A terminal for these services so I had to go from B to A. The signs for flight connections lead you that way. I did query B to B connections and I think I was told that if you wanted to it would be possible to stay in B. There was a sign not long after we got off the plane about flights within 90 minutes departing from B but I didn't read it because I never transit Heathrow, I was in herd mode following everyone else and in any case I knew I needed to get back to A. The main signage I saw was for flight connections and I believe that most connecting passengers will follow that (as I did) rather than look at the 90 minute sign.
As for segregation I was with arriving passengers all the way from the gate, on the TTS through to A and only segregated myself when I headed for the connections centre and they all went to arrivals.
Gate allocation is interesting. When I exited screening for my connecting flight the gate wasn't promulgated and there was no indication where to go so I (and others) ended up milling about just airside of security. The trouble is that if a turnaround is what, an hour, if you put up the gate before the inbound has actually arrived and occupied the gate you run the risk of having a gate change which is probably not in anyones interests. But then, how often do incoming aircraft get a stand change?
Talking about stands I was looking at the stop bars on the lead in at the gate we were using. No A 380. So I looked at some others and found one which included the 380. Then I realised that it effectively had 3 lead in lines. The primary had all sorts of stop bars (747, 757, 767, A319/320/321 and A380 from memory). Then, either side, two secondary lines with stop bars only for airbus narrow bodies. So it appears that when a 380 is not present two narrowbodies can occupy the same space.