I had flights booked to/from China using KLM's SOU-AMS connection in April and have utilised the same onward transfer previously. The reason I used it was because it was both cheaper and far more convenient than travelling via Heathrow. However, as alluded to in FrequentFlyers #1075 post, most of my friends/colleagues are simply not aware of the onward transfer feasibility so do not consider it.....and the reason they are not aware of the feasibility is because the best flight deals often only came up if booked direct on the KLM.COM website. Using the popular aggregate flight search websites, which I expect most people do, rarely gave as good offers as going direct to KLM so it is hardly surprising they took their business elsewhere.
So. with better marketing, I'm sure the route could prosper with onward transfers.
I should end with crediting KLM already re-booking (same day/EGHI) using FlyBe.....just pray I don't end top rebookng them too.