Let's face it - non-Schengen flights to/from the UK have always been a bit of a lottery when you dept/arrive in Europe
just recently I was leaving a medium sized Italian Airport for the UK and they had 2 officers on departure passport control and the processing time was horrendous - but coming back a few days later they had 8 officers on and it was a breeze coming in
I suspect that there will be no pressure at all to swiftly process arrivals departures to to the UK - ie it will not get any better than it is today - and it may get a lot worse. Any problems elsewhere will be solved by moving staff & resources away from the ungrateful Brits to the people they care about... after all who will they complain to ? the European Commission???