The 5L V8 we have now is already super cramped. Anything bigger would require some significant structural changes to accomodate.I really don't understand why they didn't start with the Tundra 5.7L unit, but hey, it's not too late isn't it?
I think engine bay space is a big factor for the next model. Lexus either needs to no longer re-use an engine from it's lineup and go all new, or go smaller and FI. Going FI they can reuse an existing engine and just fortify it.
Besides a different engine and body style, I'm expecting a lot to carry over from the current model. But yeah...who knows. Not a great deal of info coming out about it right now but speculation.