When Stelios started Easyjet, he tried to get hold of some Heathrow slots, was denied, and resorted to Luton instead. For many years, Easyjet had a perpetual message about no frills.
Easyjet is now trying to become and be seen as a business friendly airline and the focus is no longer purely on no frills.
Over the last 2 years, there was sufficient noise about them starting flights at Frankfurt, that Lufthansa felt the need to open a Gatwick-Frankfurt route just to signal to Easyjet that they should back off.
Easyjet already have substantial operations at Paris CDG, Amsterdam, Madrid, Malpensa, Munich, etc...
If IAG now have to give up some slots for Edinburgh / Aberdeen / Nice / Moscow / Cairo (with grandfather rights after 2 years), what are the odds that Easyjet apply to start flying point-to-point at Heathrow ?