Going back to the days of 'finairweb' and the blind optimism coming from most posters on there DSA should have 6xTOM and both FR and Easy based with HUY shut and long-haul scheduled flights.... I think they got the idea off Peel who, after Easyjet realised the potential of LPL, capitalised on this and therefore got well on their reputation in the public enquiry, very short sighted in my opinion.
I dont claim to know what the airline bosses are thinking but i have learnt to look at things from a common sense perspective. Easyjet probably are not interested, they tried GVA and it failed to bring in results. Add to that their base at EMA and now MAN, with Sheffield pax likely making up a portion of their support, i could not understand a reason to move north. FR are the unpredictable ones though they have downscaled at DSA on the previously daily DUB service, they seem to be doing well at EMA and LBA would be an obvious choice for a Yorkshire base.
There is very little sign of an attempt at business routes, probably due to the airports location and the filter from Sheffield to MAN where they can get to by train and probably go direct. FlyBE's BHD route failed at twice daily, i think its now 6xweekly and that is subsidised by a Yorkshire development company, not sure how long it will last.
I dont think theres any point of bringing up potential long-haul scheduled routes... A complete pipe dream.