IIRC the USG started giving everybody the "good stuff" years ago (no more SA code required), and it can be "tuned' to higher than advertised accuracy in a given geographic area. Your cell phone is better than 33 ft. It that was the accuracy you'd never be able to accurately see your lines. 10 years ago in the middle east we were getting under 3ft.
https://www.gps.gov/systems/gps/performance/accuracy/
Total system performance is more about base station receiver configuration... For instance - you have a good receiver on an aircraft, less so on a weapon, but in many cases you do a "transfer alignment" between the two which gives the weapon more accuracy than it could receive on its own.
There are also systems that use GPS, Galileo, and Glonass. More satellites, more accuracy - its just a chip and striplines on a circuit board for each group.
GPS is on the road to integrating with Galileo and the next gen of satellites - Block IIIF will start launching in 2026 - but Block IIIs are still being produced and launched at about 2/yr. That integration will likely not only increase accuracy but reliability.
You only need good signal at S/F for timing and scoring - but if things get totally automated, what level of accuracy is needed to determine a pass under yellow?
AMD hasn't done anything really new with the system since its inception (for our use at least). The. Flagtronics system is good for F&C. Seems like someone would have come up with a GPS/transponder based system that does the whole thing - might be pricey but does more, especially if it integrates with data systems (instead of the data systems doing the GPS work).
In the end, its all about standards (or lack thereof) and incentives for companies to work together (or lack thereof).
If you really want to blow your mind consider this visualization: Your GPS position is best thought of as an oblate spheroid stood on end (a football) - GPS is less accurate in the Z plane than in x and y. This football is
constantly changing shape - but your actual position is a spot
constantly moving about on the surface of the football. Now, the place you are going to is also an oblate spheroid standing on end,
constantly changing shape, and its actual position is a spot
constantly moving about on its surface. What your navigation algorithm is trying to do is drive your spot on the surface through the destination's spot on its surface....