The article is deeply confused.

It’s true that optical clocks will improve the accuracy of our measurement of time, and it’s true that GPS depends on time, but there are several steps between primary frequency standards (ie, optical clocks) and GPS, and several more steps between GPS and navigation applications.

So optical clocks cannot, in fact, have any effect on the end-user perceived reliability of GPS.

For that, the best solution is to revive LORAN which is much less susceptible to jamming. (And would also benefit from better atomic clocks.)