I absolutely agree that easy could make operations from Heathrow work profitably but this would probably mean a (temporary?) reduction at other London airports or at least little growth. I would not see the likes of Ryanair or Wizz both of which are truly low cost operating from LHR but I have no doubt that IAG would use Vueling to hold as many of the new slots created as possible at as little cost as possible until IAG's legacy operations could grow into them.