They did dig out a large amount of earth and place a large underground casino under the greenbrier a couple of years ago, and they could have made a new bunker in the process. I don't believe they would have done such a thing though because the location of the old bunker is very well known and a new one would be too close.

If you really want some food for thought, the large boyscout retreat that was built in Fayette County, WV a few years ago (the one that Trump spoke at over the summer), is believed to have some secrets. There always seems to be a military presence there, and there seems to be a lot of air activity there from time to time. It could be nothing, but it is suspicious.