After seeing some internet rumors about HD Tundras, some with Cummins V8 diesels, DRWs, etc, I'm wondering: Do you know anything official from Toyota? Do you have a link?
I think the fact the engine was in house was a big part of it, but I think the real issue was the mpg. I don't see the 5.0L getting near the mpg as the EcoDiesel. The power of the 5.0L puts it closer to the big Cummins than would likely be ideal for Ram I think. The 5.0L works well when it is the only diesel option like Nissan or Toyota.