I don't really think Ryanair really has anything else to bring to Luton.
I can think of lots...
The airport has no routes to Scandinavia, while all other London areas, serve this area. Which is one of the most affluent areas of Europe.
I can also think of numerous cities in Germany and Italy, that the airport could benefit from, especially the likes of Venice, Cologne and maybe Frankfurt.
Croatia could also benefit with some connections to the likes Pula and Dubrovnik. I never understood, why Wizz Air pulled off the latter route, I used it 3-4 times and it was full everytime.
While talking about routes, that reminded me, my mum was complaining like crazy that she couldn't book with Thomson to fly from Luton this summer to Alicante, as booked a holiday to Denia on the Costa Blanca. Ended up having to fly from Birmingham. (She is of the old school who still does packages.)
I am pretty surprised by this, and thought she was mistaken. Until I checked on their website and definitely not fly there. Would have thought this was one of the tour operators busiest destinations?!