The 6.1 or 6.4 is not likely to show up in a truck anytime soon.

The reasoning is the motor itself. The current 5.7 by itself is a high revving V8 by truck motor standards and makes most of its power in the high RPM band. The 6.1 and 6.4 rev even higher than the 5.7. If you think about it, it's not a good combo for a truck. Especially if you ever feel the need to tow or haul anything.