IIRC, from Tim Boyd's article in the "Other Mag", the tooling for the Tractors, Plows and Farm Trailers, was not part of the deal when AMT bought the other truck tooling from ERTL. So, until someone can convince ERTL to let somebody run plastic in the tooling ERTL still holds, the Tractors, Backhoe, Ect, From that tooling will not be seen again.
I'll go out on a limb, and guess that Tom Lowe, and others in the Model community have tried to get the use of that tooling, and so far have not been successful. But, maybe someday. Tim Boyd or others probably know much more than I do, as I mostly just read stuff, and extrapolate from what ahs been mentioned or guessed at by other who know more than I do.