To get to 80mppa would only require 2.5% growth - in 2017 they achieved 3.1%, so its pretty likely. To hit 90mppa by the time a new runway is planned to open (2025/26) LHR would require 1.8% growth per year so again its not impossible.
With T2 also being redeveloped
The T2 work is split into two phases (each effectively replacing the old T2 and T1). The first part has been completed but I believe LHR are waiting to start on the second phase until they have been given permission to build the third runway. They're already been criticized on costs for runway 3, so redeveloping the next part of T2 would add even more to that.
I think most airlines that operate A380's already use them at Heathrow (besides the other European airlines with A380s - Air France, Lufthansa):
Emirates - 6 Daily A380
Singapore - 3 out of 4 daily flights are A380 (other is B777)
Qantas - currently all flights are A380, but when MEL switches from DXB to PER it'll become A380 (not sure A380 can fly non stop Perth to Heathrow)
Etihad - 3 daily A380
Korean Air - Daily A380 during summer (B777 in winter)
Qatar - 2 out of 6 daily flights are A380 (others are 2x A350, 1x B777, 1x B787)
Asiana - A350
Malaysian - Soon to be 2 daily A350
Thai - single daily A380 (other is B777)
China Southern - double daily B787
There is some growth that could be made there with using more A380's, but I'm not sure how much it will actually add.
Emirates - can't really go any further
Singapore - could upgrade final flight to A380 (likely within the next 5-10 years)
Qantas - Operational restrictions prevent A380 being used. More capacity will likely come in the form of a non-stop Sydney to London flight when aircraft become available.
Etihad - without increasing frequency no scope for growth
Korean Air - Could use A380 in winter as well
Qatar - I'm not sure if Qatar have enough A380's to upgrade more of LHR's flights and I don't think they've said they're interested in getting any more.
Asiana - could upgrade to A380 (that would make it 2x A380 and 1x B787 on the Seoul route - can the route sustain that?)
Malaysian - A380's being withdrawn from passenger operations and being used for pilgrimage flights
Thai - could upgrade second flight to A380
China Southern - I believe the A380's are based at Beijing so unlikely to see an increase there
British Airways have said they're open to getting more A380's (likely second hand) so there could be some more increases there.
The bulk of growth is likely to come from either smaller aircraft being replaced by larger aircraft, but more like B757 to B767 to B777, or refitting aircraft with more seats. Singapore are in the process of refitting their A380's increasing the total number of seats by 30 or ~7%.
Bit of a ramble - don't know if all that is of interest to anyone but hey...