G-FORZ
Another pointless "What this airport needs" post. All airlines have a marketing team that are active at looking at new opportunities. If there was any potential at any small airport I am pretty certain it would have been considered.
You have hit it on the head with Wizz. They have a niche which they cover very well. There is no requirement to waste money on marketing as there load factors are acceptable and the cost of extra marketing would not increase bums on seats to justify it.
I bet if you analysed Wizz's pax I would not be supprised if you found it is mainly migrant workers and their families traveling to and from their home countries. The advantage of Doncaster is it's location relative to where they work and live in the U.K.
Like many small airports you can throw as much money as you like in development and marketing, but there is too much over capacity, and the bigger players are too well established.