The only monitor out there that would be an "upgrade" for me currently is the Apple 6K, which is far far into absurd-level purchase category.
Dell has an 8K out there (UP3218K) which, at a scant $4000, looks to only slightly less crazy than the Apple 6K @ $5000 (plus stand!).
It's a bit sad there are so few choices for us HiDPI addicts. Anything else out there I'm missing?