Ryanair already have a Luton base. easyJet have recently conclucluded a long term commercial deal with TBI for their Luton operation.
I could be possible that Ryanair would want to increase their presence at Luton, but my gut feeling is that if there are slots up for grabs at Gatwick, Ryanair would be in the running for them.
Extra slots will be available at Stansted what with Lufthansa,EuroWings,SAS and Gill reducing capacity or totally pulling out from the Essex airport.