Maybe they miss out of your prediction of the future, but I think we may well find ourselves going NOT to the extremes, but back towards the boring middle. These machines are in a managable human scale, not too far beyond the team of Horses or Oxen that defined Ag a century or more ago, and apparently of a size that is managable for upkeep, maintenance and modifications. Many castings and machine-finishing could be handled on a local level.

Beyond that, they are technically/electronically very simple, and can be built or retrofitted from VERY robust base-vehicles.

Here is a great testimonial quote from a farmer that converted an old Allis-Chalmers 'G' from the 40's to Electric Power.

http://www.flyingbeet.com/electricg/

When I built our first electric tractor, I had NO EXPERIENCE working with electric motors, and only limited exerience working on gasoline engines. That first tractor is well into it's third year now, and still working beautifully on a full-time basis, with NO tune-ups or adjustments necessary (unlike it's earlier gasoline incarnation!)

The tractor you'll be building from these instructions is even more bullet-proof and less-complicated to put together than our first machine. There are fewer machined parts, too, so if something DOES eventually break (we are farmers, after all) it should be even easier to order a bolt on, off-the-shelf replacement.

I like the gantry idea myself, and have toyed with thoughts of very light rail running between fields as well, where rolling stock would cover a span between sets of track to fly equipment over the fields (Which one would orient as long straightaways, obviously..) but I haven't worried myself with any feasibility studies on them.. just chewin' cud.