Again, I don't think Linux has generic support for overwriting (or
even describing) the operating mode of a PHY, although maybe that's a
direction we would want to push the discussion towards. RGMII to
copper, RGMII to fiber, SGMII to copper, copper to fiber (media
converter), even RGMII to SGMII (RTL8211FS supports this) - lots of
modes, and this is only for gigabit PHYs...

This is something Russell King has PHYLINK patches for, which have not
yet been merged. There are some boards which use a PHY as a media
converter, placed between the MAC and an SFP.

	   Andrew