I've looked at the USB-C spec, and it does allow for hubs like that. The USB 2.0 and USB 3.x parts of the hub are the same as for non-USB-C hubs, and the USB-PD

I've looked at the USB-C spec, and it does allow for hubs like that. The USB 2.0 and USB 3.x parts of the hub are the same as for non-USB-C hubs, and the USB-PD standard even has an example with a 3-port USB-C hub at the end.