I don't have quite the confidence Bob does.
If a truck has to pull and haul it can only go so small-engined and light weight.
A stout CVT or trans with many gears would help the little engine cope but still a person should resign themselves to Microbus-like performance with load.
A little engine working hard still needs an adequate radiator. I suspect we won't see any pickup 1/2 radiators.
A towing vehicle needs a certain amount of bulk itself so the trailer doesn't push it around. That or design it with superior balance and control when loaded i.e. like a mini-semi.
Can't speak for everybody but I'd destroy a polycarb tailgate the first day. In fact factory steel tailgates are only marginally strong enough.
Truck aero: even if you did recreate a giant Insight or EV-1, it is still... giant. It would be awesome but it wouldn't be the equal of those cars.
Call me crazy... I say if you are doing a lot of truck work you should use a truck and if you aren't you should use a car or bike or whatever. I don't know why people insist on being so contrary (like my aerial city traffic observation: everyone on n end goes s, s goes n, e goes w, w goes e.
).