Pretty unlikely. Even replacing car ECUs is not something popularly done with open source at this point, despite them being much, much more prevalent than farm equipment.

I'm sure many farmers would love it if there was an open source firmware alternative, but that's about as likely as an open source firmware being developed for home microwaves. There's interest, but it's not widespread enough that someone is going to do it well enough to make it worthwhile.

I could see it happening but you would have to convince someone to let you hack their half a million dollar machine