I could certainly be wrong but with as many diesels as you see overseas in cars (and have now for twenty years) I find it hard to believe we won't see them take over as the engine of choice in 1/2 ton trucks- as we have for the HD models. It hasn't happened sooner just because they weren't offered. IMO
The mpg, HP, torque, reliability etc. just make a diesel option too compelling. You have to wonder why if a bigger diesel makes sense in a 3/4 or 1-ton truck then wouldn't a smaller diesel make sense in a smaller truck.
Finally- Think how many of us own or owned older generation diesels (6.9, 7.3, 6.0, early 6.6, early 5.9 etc) which we raved about at the time... These new 1/2 ton diesels will offer better fuel economy, more power, and I bet far better reliability than a lot of those motors did.