The updated GSX needs the following;
Already discussed too many times already. So many times, that the even the GSX manual discuss this, because we obviously knew it would be the the most common question, even before GSX was released...
It will come at some stage, but we don't have any timeline or make any promise it will be featured in a regular update. More likely, an entirely new GSX.
Already discussed, we can change the colors, but there will be just two types.
-longer baggage loading/unloading times
Already discussed too, longer loading times means adding more cars to the baggage train, which will create all sort of issues with maneuvers into the already cramped parking spaces. And, carrying more baggage for each train, will require redoing ALL the loaders animations from scratch. AND, it will become just more boring.
If with "realistic", you mean "nicer/more complex" animation, like the fuel hose attached by people on the airplane wings, it's fairly complex, but it can be done.
If, instead, by "realistic", you mean something that actually *loads* fuel, it might work, but probably not with the most complex airplanes which might use non-standard custom fuel systems, which is what most people use.
-wing walkers on both wings
Already discussed too. This might be doable, but no promises.
-vehicles match the weather conditions
It's already there, to a point. The baggage loader, for example, gets a cover when it's raining. But we could expand it a bit.
-Southwest airlines livery
It's already there since the first GSX release.
-a booklet that tells you what company is going to support you when you arrive
As soon as you select a parking spot, the handling company is announced. What other info you need ?
other than that gsx is great but if you accomplish these you will be better that AES
Does AES has all the things you asked already ?