I've never seen such a thing - which is a little odd actually. At the moment it would be a challenge to only use only USB-C with a bunch of devices, especially with a laptop.
I have a Thunderbolt 3 dock for my Lenovo Yoga X1, it has lots of USB3, audio, DP, HDMI, VGA etc and a single USB-C/TB port you can use when it is connected. Lenovo wasn't quite as silly though and included two USB-C/TB ports on the laptop.
I guess when it is created it will need to be a smart devices to handle the power supply voltages - certainly wouldn't want to use some cheapie no/name one would you!