The problem with incorporating this into the image is that rpi-update will place your system in a testing kernel and firmware setup. You are correct that the current kernel they are testing brings a lot of improvements for the raspberry pi, and it is also a big leap for the rest of the distribution (4.19 -> 5.4) that requires more testing (for me personally, it raises a rc.local compatability fault that I can’t quite figure out, on something so basic that it should “Just Work”)
SatNOGS uses pi-gen to generate images the same way raspbian images are generated, so we want to stick to the mainline system as much as possible. I’m not quite sure how image generation would react if rpi-update was attempted in a post-install stage.
With that said, I just double checked and the current image is in fact up to date with upstream (2020-02-13-raspbian-buster). As soon as the 5.4 kernel gets merged in we’ll pick that up for the default image. I couldn’t get a good feel for when that will happen from the thread on the issue but back in April the hope was “a few months”.