USB-C displays only use the connector, the traffic then goes over alternate mode, mostly DisplayPort. For 4k@60, unless both devices support DP 1.4, then both USB3 pairs are used for DP and there's no wiring left for USB3, only for USB2.
It is almost the reverse of TB1/TB2, when a mini-DisplayPort connector was used to negotiate TB.
At least all the audio cards should be doable as external boxes.