f the federal government set up a replacement program though, and shipped all the JD machinery to Ukraine where hackers know how to modify the software, everyone but JD would win.

Funny you should mention Ukraine, a decade ago (iirc) Ukraine hackers cracked the JD interface and started making available a tool for farmers to manage their own tractors - John Deere sued

https://www.vice.com/en/article/why-american-farmers-are-hacking-their-tractors-with-ukrainian-firmware/

https://doctorow.medium.com/about-those-kill-switched-ukrainian-tractors-bc93f471b9c8

Although I suspect you already knew that :-)