Long shot but WOW Air comes to mind and are currently expanding quite rapidly, perfect candidate for a late morning arrival - departure which would hopefully enable a connection in Iceland to their new USA and Canada services.
It would also be good to see Iberia Regional expand at Luton with services to the Balearics along with some mainland Spain holiday destinations, again it's doubtful but worth a mention.
Going further afield it would be great to see more medium/long haul full service carriers tempted into Luton, again it's a long shot at the moment but I'm pretty sure it will happen one day !