I recall our old farm truck - the dump - had dual-position RE, and we had a shift lever (like the standard 4x4 lever) above the 'drive hump' ... we could shift into a very low 'grunt gear' in the RE and really get some pull-power when loaded and towing a tractor uphill. It was not a big deal to shift back and forth, although the lower gear was really low and non-syncro, so we had to stop dead to shift into or out. But once into one or the other, the gear shifting acted like any other tranny ... first through fourth, in the old GMC two-ton, with the 'granny gear' first.
As simple as it was, I can see technology easily re-creating that gear-transfer into a synchro-tranny with higher gears that could shift-on-the-fly and put what is now a four or five speed drive train into a ten or twelve speed drive train. I know, a lot of shifting, but if you think it through, once you get into one or the other, it's actually still shifting from first - fifth anyway.
I'm just as sure (for enough money) the automakers can build a auto tranny that will do it too. That means ONE gear shift gives five gear ratios each. Instead of ten or twelve gear combinations. I'm no engineer, so can't even begin to draw this out, but in my brain, it worked well on the farm for power, so I can imagine it can't work in reverse for more mileage.
Probably similar to the 'low range' vs 'high range' in the electronic 4x4 today, except instead of a power gain, it would become a mileage gain.
Probably not been into the minds of the auto-engineers until now as the price of fuel gets everyone's attention, and mileage becomes a more important factor in new truck purchase than what was once the power side of the advertising and use potential in a HD pick-up truck.
