Is it possible, using SimConnect as an e.g., to get the Default ATC text variable sent to the Kneeboard and ATC Window?
No, it's not, the only variable that can be read from Simconnect, it's the assigned parking, but not the actual path of the progressive taxi feature.
this way your program will be 100% compatible with FS' ATC and remove any problems that might arise with incursion on the taxiways for the users/AI.
No, it will only ensure the two calculated paths being the same, ONLY if you decide to accept the parking assigned by the ATC, in all the other situations, it will be useless so, it doesn't make any sense to do all that work just for that specific case, one of the most useful features in GSX is to allow the user to choose a different parking than the ATC assigned one.
Incursion problems don't have anything to do with this, the default AIs handle this by stopping when they get close to the user airplane so, it's the user that has to get around them, and there's no way to change this. Well, we changed this for our own service vehicles because, with the default AI behavior, they couldn't get close to the user airplane for servicing it!
It can also function as default so that instead of the pilot/user having to (using the GSX Menu) always know where to park specifically (at a spot/on the ramp). He/she seemlessly communicates with FS' ATC and GSX makes it happen transparently to the user
This can be probably done, if you don't do anything, GSX might assume you selected the default ATC assigned parking. However, right now the GSX menu is a two step selection, first it asks which parking you want to go, then it asks if you want a Follow Me car so we would need to change it a bit, to make it transparent with the ATC.
BTW: You've never said that ParkMe was going to become GSX before now; we were always led to believe that ParkMe would become its own tool just by itself, like XPOI.
Which is exactly what is happening: ParkMe IS going to become a tool by itself, and that tool is called GSX. Or, are you trying to say that, by changing its name and adding other features too, it's not a separate tool anymore ?