With the basic function of the TS hitch, you manually add air through a Schrader valve on the hitch, when hooked up to the trailer. You inflate the bag enough to bring the load beam up to the index mark.
I am curious as to what benefit having a gauge and switch inside the cab would do for you?
Now, adding a leveling valve would seem to be a very nice upgrade, as then you would automate the process described above. But again, I can not think of any situation, such as road conditions, where you would want to adjust the air in the hitch, on the fly, from inside the cab. IMHO.