Thunderbolt devices are currently a joke. The use case would be being able to push a laptop's GPU out to an external display card, so when you're docked you can run whatever desktop GPU you want.
But the cheapest connectors for that sort of thing can't to x16, and cost $800. Which, for the price, would let you buy an entire desktop.
The use case would be to connect to the dock with 1 cable rather than a huge port on the bottom. Or connect to an external drive bay for fast and low overhead access.
The external GPU thing has always been the most fanciful use case.
But the cheapest connectors for that sort of thing can't to x16, and cost $800. Which, for the price, would let you buy an entire desktop.