Tom, I don't know if this qualifies, but the eighth green at Pebble seems to becoming more and more unstable, sliding ever so slowly.
How about the unmaintainability of clay ridden soils? Poppy and Spyglass Hills, being examples.
When I toured that lower section of black mesa, Pat and I came across the beginings of a trickle of erosion, in the silty sand. It was occurring near the end of an imagined landing area. In my amateurish manner I envisioned a feature that was designed to evolve naturally (gets wider and steeper) causing the hole to change slowly overtime, and IMO for the better. In other words using the expected rath of mother nature ,to do the work of the D-whatevers.
Since that area has been untouched, forever, and most of the features of the entire site were formed by rushing waters, it brought safety concerns, directly to mind. Not a problem for me, since I value a certain element, and level, of risk, should always be part of the sport.