Can you expand on how this would come to be, in practice?
Because yeah, that's what you do when you recoup the rest of the cost in the subscription/maintenance.
It's the same model that game consoles use to keep the hardware costs low. They make it up in the game and peripheral licensing fees.
If JD dropped the subscriptions, but instead charged full price for the tractors, people would just scream about the prices instead.
I actually agree that farmers should legally be able to repair their own tractors, or have anyone else do it. But gaining that "right" back wouldn't actually fix their complaints, just shift them.