I'm gonna second the diesel electric theory. Already making a huge resurgence in the commercial marine industry and now starting to creep into the construction equipment as well (Cat dozer). Actually, all the large LeTourneau mining trucks and loaders have been diesel electric for years, haven't they? There are so many more electronics in the tractors now, and the electric over hydraulic controls are fantastic. I believe John Deere has at the very least a prototype diesel electric tractor. Diesel engine only puts out the power it needs for any given task and no more. Electrically driven hydraulic pumps for drive motors, electrically driven pumps for hydraulic remotes, and an electric pto. Super efficient, compact, and pretty reliable stuff. Electric motors allow for precise and instantaneous control. In some ways I believe it is easier to build a machine this way also.
Give it another 10 years and I guarantee it will be more prevalent - if for no other reason, than it will cut down on emissions by allowing tractors to be operated on less horsepower for the majority of their tasks, only taking advantage of their full rated diesel engine power when a full electrical demand is absolutely called for.
Guys, don't be confused - the tractor doesn't run on batteries - it still has the diesel engine which runs ALL THE TIME. It just drives a generator instead of a gearbox which then distributes the power to the different electric motors. For instance, each drive wheel would have it's own motor (no drive shafts or gearboxes) and would only get the power that is called for. Think - truly independent 4 wheel drive! Much less wheel slippage as power can be split between the other non slipping wheels. You'll be able to run your pto slower without affecting ground speed/wheel power or hydraulic flow - everything is independent.
Thoughts?