Will the costum(s) pushback be an extra line in the menue? like:
No, only the straight pushback will be. The custom pushback works like is working now at those FSDT airports where we enabled it, up to two entries will replace the Left/Right default entries, with a custom label you can define as you please, such as:
"End on Taxiway A, facing North-East"
"End on Taxiway A, facing South-West"
With those matching the coordinates of two existing AFCAD nodes that will act as targets for the final destination. In this context, Left/Right don't really have any sense, when you customize with a custom destination, they will just be like an Option 1/Option 2, with a customized label. Since you can insert the coordinates of any AFCAD node, nothing would prevent you to make a custom pushback up to the runway...and the coordinates don't even need to be 100% exact, since the closest node will be then used, so it should work even it the AFCAD is edited.
GSX always had this capability, we are now allowing users to get access to it in the scenery customization file.
GSX has *far* more customizations capabilities that most of the people think, the typical opinion is that GSX has a "generic" approach, while other products are "custom", thus more "realistic."
In fact, what's is really difficult, is making a generic program that works everywhere, because, of all variations and quirks in the AFCADs, and all the problems related to automatic pathfinding, fitting approach curves that must be calculated over random and sometimes erratically placed AFCAD nodes, especially at 3rd party airports (and we put ourselves to have been in the "guilty" category sometimes, as scenery designers, but we tried to improve, after GSX...).
Making a program that *requires* to be tailored to a specific airport, instead, is far easier, as a program, but it will then require a lot of work to support each airport, so you are then forced to charge for it. We are taking the approach that, instead of charging per-airport, we'll allow users to do more and more customizations on their own.
Next one, we'll likely open up the ability to customize the marshaller and docking system parameters, so anyone will be able to place those in any scenery they like, and setting stopping distances precisely. This is a bit trickier though, because it really needs an easy visual editor without having to type coordinates or measurements.
This of course will apply to 3rd party scenery developers too, that can add value to their products for free, and without having users spend any extra money, to enhance their product, by simply providing their sceneries with a GSX .INI file to go along with it, and they can do it on their own pace, so they can have it ready for the scenery release.