We'll try to make it as reliable as possible first (as a duty to existing customers, that always come first), but we'll also try to add all the features that has been discussed in the forum over the years.
If something hasn't come yet, it's only because there are other things to do first, but that doesn't mean that we don't internally discuss every suggestion and, in fact, most of the latest new features, were all being suggested by our users.
New services, like water and lavatory will come, for example. Pushback will be constantly improved too, and some areas like refueling really need attention.
The airplane configuration editor will be more powerful, because it will allow to specify more points over the airplane we cannot get in any other way, for things like water supply, refueling points, engine position to place traffic cones correctly, etc.
The scenery configuration editor will one day allow you to place an FSDT docking system on any scenery, default and 3rd party. In fact, GSX is already internally ready for it, it's just the user interface for it is not the easiest thing to do.
We are also working with Jeffrey Stähli, the author of SODE, and are well on the way to integrate GSX with SODE, and make them easier to use together (no need to select a parking twice, in GSX and SODE). This will probably have some effect to our sceneries too.