For me the way ahead is to stick with the simple MII-driver and just make sure that
features such as pause configuration are properly implemented. Please tell me if that
makes sense or there are better ways.

The better way forward is to refuse to support the device in Mainline,
until the vendor produces a firmware version which is not FUBAR.

The PHY ID is a contract, it states compatibility. If different
firmware gives it a different API, it must have a different ID.

Mainline can push back on vendors. We can say only their out of tree
vendor crap driver will be used with their hardware, if they don't
follow the basic rules as defined in 802.3.

There are plenty of USB dongles what just work in Linux, because they
follow the rules. So i don't see it as being a particularly big loss
to Mainline.

   Andrew