While that is of course technically true, we are living in an imperfect world and USB Ethernet controller implementations should probably be aware of those mill

While that is of course technically true, we are living in an imperfect world and USB Ethernet controller implementations should probably be aware of those millions of switches out there that use a handful of switch chips with known bad implementations. Keeping to whatever the spec supports is nice, but if the world doesn't work that way you still get a broken product at the end of the day. Instead of pause, it should (at least have the option to) disconnect. Ethernet link training isn't a computationally expensive and lengthy process anymore, at least not from the user's perspective. Between plugging it in and moving your hands to your input device L1 and L2 are up before you even get a chance to look at your display with L3 being available pretty quickly thereafter.