> Determining when a device is on a metered connection or not is the tricky option, probably inpossible. Perhaps something device manufacturers could incorporate into network settings (a metered/non metreed flag on the connection)

I think that your second sentence contradicts your first. Making the determination automatically is, indeed, probably tricky; but making the determination by consulting a user-set flag is trivial. I'm too wedded to my Mac to commit to a Windows machine, but I love that Windows 10 has such settings (necessary to prevent it from auto-updating), and wish I could make my Mac do it.