A lot of missions use their own implementations of a virtual garage, and non comes close to the UI of the virtual garage, but after trying to
use it in a mission I can understand why nobody uses it.

There is two simple features I think would accomodate everyone:

1. Be able to pass in an array of available vehicles.

Also, be able to pass in an array of vehicles that cannot be build but can be looked at in the VG.
(lots of missions have a resource thing, where you would need a certain amount of something to build different vehicles.
That check could be done before opening the garage, passing the ones you have enough resources to build into the spawnable list,
and the ones you dont into the disabled list)

2. Return the created vehicle so the missionmaker can reference it in a variable.

Something along the lines of:

_createdVehicle = ["Open",[ true, _vehicle ]] call BIS_fnc_garage;

So that I can check what they build and do whatever I need to do (subtracting resources based on type of vehicle built)