The only serious contender for LGW has to be Norwegian. Ryanair could really spice things up on Belfast but highly unlikely... I wonder could easyJet avail of the slots to launch a Gatwick Belfast City route ( and I already appreciate that they've tried LTN BHD before, though given the lack of slots, this could be attractive).
As for Dublin I cannot see any wisdom in any airline touching the market.
EI-BUD