You'd have to be mad to leave a command at easyJet on the assumption that you could get a BA Heathrow command after 6 months. There's absolutely no guarantee of that happening and even if it did, you would take a massive pay cut to do so. Over on the easyJet DEP thread, someone has posted a very comprehensive review of the Captain package at easyJet. It is significantly better than the BA package on pay point 1, and for many, many years thereafter it remains better, especially once you factor in the share schemes and bonuses that easyJet pay. Not only that, but your lifestyle would take a major hit for a long time as you ended up flying blind lines with no roster control (to the new EASA FTL limits!).
If, however, you want to go long haul then clearly there is an argument that now is a good time to make the move.
As for low cost short haul being the future, the term "low cost" would be better replaced by "low wage". The future of short haul is increasingly in the middle ground in terms of service. Passengers want some extras like frequent flyer schemes and newspapers and wifi etc. Even "low-cost" carriers like Vueling are realizing this. The key to providing it all at an attractive price is to ruthlessly drive down labour costs. The incoming Executive Chairman of BA wholeheartedly subscribes to this view of the world and will doubtless drive forward its implementation.