EasyJet's whole development has been based on taking on the established carriers in city-to-city routes. Serving oddball points, Ryanair style, has not been part of their model.
Likely initial offerings for them from Heathrow would be Glasgow, Edinburgh, Amsterdam, Madrid, Paris, Nice, Athens, and such like, a small selection of good business yield routes where they have established strength at the other end as well, which they could move on to serving multiple times daily, at less than BA fares.