The trouble is, unlike at BFS, the equivalent Translink bus service from BHD is just fine for getting to Belfast - 10 - 15 minutes to town and it's not unreasonably priced.
At Aldergrove the cost of a new station would be much more (as well as re-establishing service from scratch on the mothballed line) but it could at least offer significant rush hour journey time savings over the bus, which has to deal with the M2. I frequently fly in before 08:00 and spend more than an hour on the bus getting to town.