Another thing to note on the accuracy front is that the US is about to start launching the next GPS IIIA generation, which has higher resolution than the current generation.
While the features of IIIA are nice, it will be a while until all the existing ones are replaced by IIIA.
The more immediate nice thing about the IIIA launches are that it adds more satellites that can transmit the L2 signal. Currently there are 18 healthy IIR-M and IIF satellites which can transmit L2. I believe you need about 24 minimum for full coverage.
Once we have full L2 and we get civilian dual band L1/L2 receivers it will get rid of one of the biggest sources of inaccuracy which is ionospheric delay. A dual band L1/L2 receiver will be able to measure ionospheric delay directly. This means the delay calculated will be for that specific point instead of the area covered by a WAAS ground station. Plus you won't need a direct view of the WAAS satellites.
https://en.wikipedia.org/wiki/GPS_Block_IIIA