There's not a good reason for Toyota to build a diesel. Toyota is going hybrid and EV options for all models by 2025. Hybrid gasoline engines can run with unequal compression and exhaust strokes that net around 40% thermal efficiency. That's about the same as a diesel. The hybrid system solves the low torque output of those unequal effective stroke designs. So a hybrid gas engine is nearly as efficient as a hybrid diesel and costs a lot less to produce. In countries where diesel fuel is more common and usually significantly less expensive and emissions systems are not currently regulated in the same way - sure it makes sense. If the cost of a DEF system is similar to a hybrid system - in the USA Toyota's almost certainly going to opt for the hybrid.
Would a I6 gas or diesel be great? Yep. Toyota is just soo conservative it's not likely to happen. If they aren't even willing to put a v8 in the 4Runner that they already have and already sell in the same platform, I can't see anything exciting being very likely.
It's very unlikely that the emissions rules are going to get less strict. Jeep is also building an EV wrangler and a hybrid. Those are the future of the wrangler. I love the big v8 wrangler idea - but I think we all know it's going to be short lived. But hats off to Jeep for at doing something great when the window is open to do it.
I think we'll be left dreaming of a turbo 6, hoping for any sort of 6cyl, and getting a 4cyl. I might driving a turbo 6 or v8. It just won't be a Toyota for the first time in a long time.
