We're not going to go down the path of training a bunch of highly specialized models for tasks like "this tractor should tend this field".

We're going to (and are already on the way to) train deeply general models that can be told: "go tend that field."

And if that's the case, it no longer makes sense to build specialized, purpose-built tractors to house that level of autonomous capability. You instead put it in a humanoid frame (with a little extra sauce for locomotion of said humanoid), and get that to drive your existing tractor.