Looks like I was right about the price. I finally stumbled across this device. It's not even slated for release until the end of next month, but it does most of what I was looking for. It's a Thunderbolt 3 dock.

The only thing that I don't like is that it says it only does a "trickle charge" for the connected laptop instead of a real charging solution. Sounds more like it maintains battery levels instead of trying to top them off.

*edit*

That Dell dock you initially linked to is also a Thunderbolt dock, but I don't know which if the scenarios you laid out either of these docks are using. But it sounds like driver support might sink these kinds of things.