...KLM might have made it initially pay, with their significant route network, utilising 50 seaters but KLM don't operate anything smaller than 80 seats these days and those don't have the performance to operate to/from such a STOLPort.
I wouldn't be so sure about that. The only reason KLM pulled put was that there was precious little in the way of radar cover and get they a bit twitchy with things like that. Both the E190 and F70 could lift economic (but not full) loads out of SZD but they need the traffic to do so. Also KLM are unlikely to have a problem allowing FlyBe to feed into AMS, if they chose to operate into SZD. But I think the fat lady has already sung.
PM