The driver for commercial aviation to use GPS is the money they'd save in no longer having to maintain those ILS and beacon systems.
There are two distinct lots of people who are in this: the airlines, and the "national air traffic services" who maintain the ground stuff.
The airlines have to have all the kit anyway; unless you dedicate a plane to a single intra-EU route all its life. The last thing they would want to do is "pay as you go" extra for a GPS approach.
The incentive for GPS approaches would be in the navaid maintenance group. But they would still need to force all airliners to equip the planes and retrain the crews. We aren't talking of US-style GPS approaches; these are GPS guided precision approaches down to 200ft or less, down to Cat3c. This would take not years but decades.
If Galileo was meant to be a play on this, it would be a very long shot. Also Navstar isn't going to stand still all those years; it will get better, more powerful (better S/N ratio).
If savings are obtained by decommissioning navaids and landing systems, would those savings be passed on to airlines in reduced en-route charges? I think the answer is obvious
I bet the direct cost of maintaining say the ILS at Heathrow is an insignificant part of the money which an airliner pays to land there and unload its contents.