It's not fast enough. USB cannot drive a 4k monitor at 60hz. You can use the physical interface to do it, but this uses Thunderbolt. This means that the dream of a one-cable-for-everything setup is not here yet, unless you use a Thunderbolt dock, which multiplexes the USB stuff in with the monitor signal. A thunderbolt dock costs around 10x more than a simple USB dock.
To be honest, I'm not really sure why this is necessary. I don't see why couldn't have two interfaces - one simple/moderate-speed one for most use cases, and a fast one (which could incorporate the slower one) for when it's needed. Trying to cram everything into one interface seems to introduce too many compromises (I no longer know what the port does) and a lot of complexity.
the point is you shouldn't have to know what the port does, it should seamlessly interconnect. you shouldn't have to be thinking about wires etc. it's like how bluetooth somewhat seamlessly interconnects across generations of bluetooth. that's how all standards should be
USB-C is already there up to 4k@30hz, and none of the stuff you're saying is true, unless you consider current USB-C cables insanely expensive. You can get a USB-C dock that provides power as well as the ports you need on one cable for ~$60.
