I've been flying quite a lot with the low cost carriers recently. It's hard to think of new services they could provide that I would actually pay for.
Most of the time I travel with hand luggage only to avoid waiting around for baggage reclaim.... only to find a long queue at security/passport control both on departure and arrival. On one occasion we had to wait outside in the rain at Eindhoven.
Perhaps they could fund some extra passport control officers for the exclusive use of paying customers? Ideally I'd like to be able to buy a book of "get out of jail" cards and choose when I use them depending on the length of the queues.
Some form of season ticket or discount for a book of 5 or 10 tickets on the same route might also be of interest.