I am not sure what a Gen 4 G30S will give that isn't already on the Gen 3 G30S. The current one uses the SF frame, which I have read is the basis for the Gen 4 large frame, before any of the pin-on back-straps are put in place.
The current G30S has what looks like the same new recoil spring that they are putting into the Gen 4 pistols. And I cannot feel any difference in trigger pull when I compare my Gen 4 G19 to my G30S, which is not Gen 4. Yes, yes, maybe a little bit of apples and oranges comparison there, since those models are not of the same frame size. But the triggers feel the same.