There have been a lot of threads talking about the graphics, etc... I think anyone who plays it and enjoys it agrees that it more than has it where it counts.
There are only two things that stand out to me in as far as what makes it look dated...
1. The biggest one: The extreme low poly-count terrain. I have no idea what goes in to changing something like this, so I may be way off base in suggesting that it could be done, but cutting down the massive pyramids... smoothing out the razor-edge mountains... not even anything major, just adding some more faces to them... it would have to be a lesser frame rate hit than the new clouds, right? The textures do an admirable job at hiding the pyramids, but flying in the canyon REALLY makes it obvious.
Having smoother terrain would make it a little nicer for the GVrs to get around as well.
2. Secondary, but definitely noticeable, the repetition in textures... for example, if you look at the runways, there are awesome tire marks... uneven, right where the planes land, they look great... then they are marred by the repetitive underlying texture that shows up as an unmistakable pattern at medium to close range.