will we see more long haul as airlines start to hedge their bets and want to secure more slots before the full sign goes up at Lgw as well.
Yes - we already are seeing it, long haul growth at Gatwick has pushed out short-haul growth already for Summer 16. Gatwick want this of course and their pricing policy is being geared towards it. The only other game in town for long haul is Stansted and most really don't want to go there yet so expect an increasing long haul slot grab at Gatwick over the next few years.
This will be in addition to, not in place of, the Heathrow situation that Rutankrd describes.