No, this is not true. If you,
then, if USB is actively being used downstream (from the hub/dock or within/from the monitor), half of the USB-C transmission streams will be unavailable to the monitor because of this USB support. This will result in the capabilities of the monitor being restricted. Now, this is really only an issue if a 4K monitor is being used. In this case, it will be limited to 4K@30Hz. If you are connecting a 2K or lesser resolution monitor, it will operate just fine at 60Hz (and perhaps even higher frequencies).
Regarding the second question, no NUC models support USB-C-based Power Delivery.
Thanks so much, that's good to hear.
So this would actually be a good reason not to go for a 4K display then. Do you think WQHD (2560x1440) would work at 60Hz when using USB-C with the hub at the same time? Is there a way to tell for sure (other than just trying)?
DisplayPort 1.2 has a maximum data rate of 17.28 Gb/s. Half of that is 8.64 Gb/s.
According to the chart (here: https://en.wikipedia.org/wiki/DisplayPort), 1440p@60Hz only requires 5.63Gb/s. Yup, looks like that will work just fine. In fact, 1440p@85Hz only requires 8.07Gb/s, so there is a possibility of that working as well (though that may be pushing our luck).