It's not possible, since the menu can only hold 10 items at time. Normally, parking gates are grouped by terminal, so you shouldn't see a very long list. In fact, a very long list is what you usually see on the standard Go To Airport menu, and GSX is improving on that, by splitting gates by terminal.
Of course, in order for GSX to be able to group parkings by terminal, they must be grouped in the scenery AFCAD to begin with. If the scenery is made with all parkings under the same group, GSX cannot possibly know how to divide them.
Yes, with our airports we can rearrange the grouping in an entirely different way than what the underlying AFCAD tells us. But this is not accessible to users, because it would be quite a complex interface to create new groups, rearrange them, create special rules to display their names, etc.
It's all possible, but only through scripting language, so it works only at FSDT airports.
If you could tell which airport has hundreds of parkings on the same terminal, maybe we could make a custom config for it.
