I can’t tell you what things will be available / needed in the future, but I am certain it will be as different then compared to today as today compared to what was.
Nothing - even a G3X - is the last and final thing that anyone will ever need.
We no longer have the VORs and ILS approaches we used to have. Something will replace GPS. Things always change.
I'm sure that's true with respect to navigation. The changes will probably be relatively slow, though, just because of the cost and lag associated with swapping out the gear in airliners and the military. I think it's just jamming of GPS that has caused the FAA to maintain the almost functional VOR network.
But for just flying a piston single VFR, really just airspeed and altitude indicators are needed to fly, outside of compliance. A tach is a nice bonus, and for many you really don't even need airspeed and altitude, but they're handy. As far as I know, if they still work OK you could be using an airspeed indicator and altimeter from 1940 and be fine, if they still worked, that's 85+ years.
So back to navigation, now we have VOR/ILS and GPS, disparate systems, that manufacturers have been able to combine to let us navigate pretty seamlessly switching between the two. That a nearly 20 year old 430W can do that is pretty cool, and I think it means that any new navigation system would be something that could integrate with whichever is left of the other two. I'd kinda like to see inexpensive ILS added to the integration, but that's probably unrealistic.
Anyway, all of that should fit into a single display, and any of that is going to require the same updates they do now, as approaches and airports change, and as the routes/airways change.
I'm not sure if I had a point with all this rambling, except that I'm pretty sure we'll be able to fly VFR with simple stuff for a long time, and the current system isn't going to change any faster than the ability for old 737s and C-130s to fly around everywhere in the country IFR with their current equipment. That, and if I ever have any airplane, and it has glass, I'm going to probably want that analog ASI and altimeter, because I know they'll work even if I don't pay the electric bill.