Whilst I can see the reasoning that KL would have a larger catchment area at DSA, the point is the services into HUY are doing great so why fix what ain't broke?
Regarding the old Air UK F27 loads on HUY-AMS, those figures don't really mean anything today. A couple of years before then the service routed LBA-HUY-AMS, thrice daily with F27's. Now LBA has 5 non-stops each day with 733's and F100's from LS/KL and HUY has 3 F70's each day. The markets have changed beyond recognition as air travel has become more affordable over the past 20 years. Whilst I can't vouch that every single seat on every flight is taken, people I know who have flown on HUY-AMS have always said that their flight was completely full, giving the general impression that it is a consistantly good performer.
On the LCC side of things, it does look as though they may have missed a golden opportunity but I still believe that a carrier such as Flybe has the right sized equipment to offer a competitive and successful operation from HUY. Just because DSA will be open for business doesn't mean that the people of the East Riding of Yorkshire and North Lincolnshire will want to use it in preference to HUY if they had the choice.
A little further down the line, Eastern Airways will be phasing out its J32/J41 in a couple of years time and is supposedly looking to replace them with aircraft in the 50-seat range. Given that they may be tempted to reduce their high fares a little to put more bums on seats and that their new aircraft will be more comfortable over longer legs, they may be tempted to start new services from HUY if another carrier doesn't step in. Perhaps EDI/GLA, CDG or DUS?