This is exactly the proposal that was floated a couple of years ago by the developers behind the new stadium and sports complex that would have sat south of the railway line in Sydenham. Their planning application proposed a new railway station (often called a 'halt' in NI to calm politicians nervous of any captial expense) on the site you've identified, with enclosed footbridges (like Prestwick) to both the airport terminal and the stadium.
They seemed to hint that since they'd both benefit, they could share the costs with NIR, DRD etc. However that plan seemed to evaporate.