What two more "good" airlines can they get? Really they already have the only two that will operate a *network* out SEN and carry a large number of passengers; so the realistic hopes are that those might grow.
The rest of any increase will most likely need to come from airlines (perhaps those similar in Nature to Adria) adding individual routes. We can all create a long list of airlines that *could*, and as time goes by maybe some of them might!