It is still correct for the end user to expect that. If you make something that breaks the expectation it should be your fault. A connector is a connector, a cable it a cable. If they all physically fit it should just work, and whoever broke that should be legally at fault. Now I will admit that cables break, and connectors wear out, both of which are not the fault of the manufacture. However it should just work.

Note that if you connect two usb-6 devices with a usb-5 cable (Intentionally using standards that don't exist yet) is may drop back to working like usb-5. If you connect a usb-5 device to a usb-6 device it should all just work - to the limits of usb-5 of course.