I think everyone is
I think everyone is forgetting the market. When you account for the cost of Diesel, with additives in some places to remain compliant, the upfront cost and time value of money over the loan, a hybrid auto makes more sense for the Tacoma.
Why?
Broader market. Like all manufacturers, Toyota is not in business to fulfill dreams. They are in business to make money. For every Tacoma, or any pickup for that matter, that is "worked", I'll show you two that are washed weekly and are basically an car in disguise. Most never carry more than 100lbs of anything...ever.....there is simply a bigger demand for a Tacoma, at 31mpg hybrid auto, than there is for a 4 cylinder Diesel.
Is there a market? You bet. But, in the US, we don't typically drive on dirt main roads, do we? We zig and zag through traffic going to and from work with nothing in the beds of most pickups. Make a Tacoma getting anywhere near 30mpg and I'll show you people lined up at the door to buy one.
Toyota has THE best hybrid system, period. It's reliable, smooooooooth, and most of all, works. The truck can carry more than enough batteries (Finally, a payload...) to offset the weight....use the standard Tacoma engine or that 156 HP one (circa 2006???) with a Hybrid setup to keep production and manufacturing costs down and I'll show you one great hybrid PU that 3 out of 4 Tacoma buyers would drool over.
A fun truck, with GREAT mpg, that is reliable and most of all, desirable. Like all Toyotas. Make that, produce that, manufacturer that and I'll watch the ever piss poor American made compact trucks disappear in two years....sure, they will make hail mary rescue attempts and it will show in their typical goofy manufacturing and details....they are fine for larger trucks (Somewhat) but, for compacts? Please.....
Make a Toyota 6-7 speed automatic (not that dreadful CVT) Tacoma Hybrid and watch them fly off the lots...target price? Around 25K (Remember, they will be using components already tested and true...namely the 156-170 HP 4cylinder with their synergy drive...god knows, the truck can haul the batteries....modify the bed to put them just underneath the front for lower center of gravity)....
Make that and it's game over.