Maybe for overseas? The foreign market for diesels is very robust. Not here.
I don't expect a 3.5l twin turbo to solve much of anything. Ford's gets about the same mpg as their V8. I see it as more of a lower cost way for Toyota to do an engine upgrade and get ~10% boost in mpg (vs upgrading the v8), since they have a similar engine in a Lexus. Like Ford's I expect it will have more low end torque which is nice.
Both of my Tundras barely got 18 mpg at 70 mph (had to baby both of them while accelerating and passing). When it was stock my 2.7 F150 got 24mpg at 70mph with zero effort (leveled, larger tires, 3.55 gears dropped it to 22mpg). At 65 I could get 27-28 mpg.
The 2.7 gets better mpg than my 1st gen Tundra (6 vs 11) ever could while towing a travel trailer and absolutely humiliates it when it comes to pulling power. It also gets 2 mpg more than my 2nd gen Tundra did while towing the same travel trailer and has much better performance.
My agency had a couple of F150s with the 3.5 and the 5.0. They were all 2wd, super crew, XL, 3.55 gears, and loaded similarly. The 3.5 always won when it came to unloaded mpg. Towing the 3.5 would either get the same or 1-2 mpg less than the 5.0.... Buuuut it pulled so much better. The extra power in the lower RPM range of the 3.5 made the 5.0 seen neutered.
Part of the "problem" with he EcoBoost fuel economy is it's so very easy to use the low end power, thus it uses more fuel.