I imagine farm is probably done. It seems to have been handled like a one-note short-lived theme: numerous sets at the beginning and then tapering off with just a few second year themes.
If it were to continue, I would like to see sheep, a farm house, a proper barn, and some kind of fields for the tractor to work in. I've also always thought an orchard would be a nice set/MOC...
I'm also surprised they didn't do a crop-duster, give Lego's penchant for biplanes, though maybe its not eco-friendly enough for Lego?
Steve