easyJet tried and failed LGW for 12 months (2014-2015), and it is unlikely that they'd try again. British Airways have been cutting back their domestic operations from LGW for years (NCL was axed in 2007), instead focusing on leisure routes. Both Jet2 (2007-2008) and Flybe (2008-2014) operated the route, but neither are likely to recommence operations.
STN has also been tried and failed. GoFly/easyJet operated the route 2001-2010, and then Flybe gave it a go 2015-2016. Ryanair would be the only viable candidate, and even they are unlikely to commence operations given their disinterest in their UK domestic network.
Wizzair do not fly any UK domestic routes, and it would be very unlikely for them to begin now, especially to an airport not already served by the airline. easyJet are also unlikely to commence LTN flights, given they've tried and failed flights to both Stansted and Gatwick.
LCY was operated by Eastern Airways for a short while in 2006, but has since been untouched. Cityjet would be an unlikely candidate, given that they only operate one route (LCY-DUB), and are focusing on their leasing and franchising business instead. Flybe are also unlikely to operate the route, given that neither London City nor Newcastle are aircraft bases. The fact that the route would require an early morning departure to London means that a W pattern would also be unfeasible.