I would not mind having a 30 HP gasoline motor in my CUT one bit. And no, it wouldn't necessarily need to be turbo. Just 1.5L to 2.0L 3 or 4 cyl that revs up a bit higher - but it would still be quieter, just as durable, cleaner exhaust (even T4 CUTs are kinda stinky) with no DPF regeneration, and $4/gal fuel instead of $5.50/gal.
That said, it makes sense why they all stuck with diesel. The DPF addition was a relatively minor change on this type of product that gets minimal engineering investment for "new" models. Stick with what works, etc.