There's a great deal of communication that happens outside the operating system, and a bunch of different multiplexing modes and things like that. There's at l

There's a great deal of communication that happens outside the operating system, and a bunch of different multiplexing modes and things like that. There's at least 4 different speeds it's going to need to talk at (1.5mbps, 12mbps, 480mbps, and 5gbps) with a good deal of synchronization and other bits. There's a rather decent amount of logic that has to be implemented, and I wouldn't be shocked if you end up needing what basically amounts to another CPU for the controller itself to manage the entire connection and negotiation. Depending on the physical construction it might also need some decent power transistors if it's also handling the 2 amp current limit on usb3.0 internally (rather than signalling ones outside the chip).