Larger capacity aeroplanes. For example SQ is going to A380s for all of their 3 daily flights. I would imagine that a number of European airlines are going to be substituting some wide-bodies for their regular flights.
In addition a lot more visitors, from visa required countries, are going to be coming increasing the average dwell time significantly.
While I recommend avoiding Heathrow at the best of times, these will not be the best of times. You would be insane to enter the UK here. Try Bristol, or Southampton, or the Orkneys.