You do need to separate what people say they want with what they will actually lose. Too many people have very little idea about airports and routes and seem to think it's grand and easy to just start up a 13 times daily service to Amsterdam/Some airport in the middle of eastern Europe that nobody has ever heard of that has fares of €2.99 simply because it's a lovely destination and they can't see why everyone wouldn't want to go there.
Basically, while we get a perception of a strong demand for certain routes, most people won't use them and complain about price and frequency, or the airline, or the airport or the transport to the airport blah blah blah.
KLM in the future could try SNN-AMS, I could see that being a viable route, but I doubt it'll happen currently
My thoughts are stick to FRA with LH and try get that to a workable frequency.