southside, slot availability and movement caps are two very different things.
MAG could be successful in getting an overall cap raised, but that doesn't magically release some extra slots between 6-9am when there are none, or in the increasingly congested 9pm-midnight period. So pabely is right in that there can't be an explosion in based aircraft, although there is still plenty of availability before 6am and after midnight which would still suit the way Jet2 operate. Those sorts of slots have been widely used at LGW for some time. Even Ryanair now have some arrivals well after midnight, previously they've had nothing scheduled to arrive after 23:55.