I think it's time to upgrade my ancient (by digital camera standards) D3, but the D5 is too pricey and i would like something a bit smaller to lug around. The D850 seems like the obvious upgrade, but I know that there is a replacement coming.
I can afford to wait six months, maybe longer. I'll get either the replacement or else a D850 at a discounted price.
Let me make sure I get you right: you're hanging on to a model that was introduced 12 years ago and discontinued seven years ago because you THINK the D850, king of the hill in Nikon's portfolio and introduced merely two years ago, will get a replacement at some point.
I KNOW there's a replacement coming for pretty much EVERY camera in the market at some point. When that will be is left to speculation. There is no D850 replacement in sight, and I think Nikon would be foolish to tackle that any time soon. They've got more urgent upgrades to take care of, with a D5 replacement (announced but still vague) and D750 replacement near the top of that list. Not to mention that they need to continue expanding the Z line.
For my part, I cannot think of a single reason why I would want to wait for a D850 replacement, or what I would even want in a D850 replacement. Maybe except half the size and weight. ;-)