Back in the mid 90s when GPS first achieved IOC and shortly after FOC the FAA's future air navigation system (FANS) actually envisaged the shutting down of all terrestrial nav aids ( ILS, VOR, MLS, ADF ...) in favour of GPS as sole means within a decade or so ...
Of couse WAAS and the GPS constellation, plus infrastructure, have come some way towards that end but how ever did the FAA ever even entertain such notions is quite unbelievable today. Talk about putting all your huevos in one basket? No wonder it all went pair shape.
GNSS has now moved on from the technical challenges of the 90s but these have been replaced, now that the world has woken up to realise the importance of this utility, by political ones - the outcome of all this is that GNSS will sooner rather than later cease to be a free asset not only because of the need to fund its upkeep but to capitalise on it. The Military will by then have evolved their own successor system leaving the civilian world to fend for itself. The Europeans have traditionally levvied tax or fees on everything, Galileo will be no exception and GPS will follow suit.