Giles, I don't think anybody at the Airport will be having sleepless nights about it.
Ryanair haven't really taken LTN seriously regarding expansion although they did hit 5 based for one year a few years back.
Not sure why this is so , maybe relates to relationships in years gone by! maybe LTN just doesn't want to be held to ransom in pricing.
As you say the slots would be snapped up anyway.
i am wondering more about SEN possibly diluting STN catchment in Essex and surrounding areas for RYR.
Whatever RYR will be getting a sweet deal at SEN.
LTN does need a couple more airlines operating though, they can't seem to retain them. Transavia, Atlas Global and now possibly Vueling to name a few.