That's my issue with the new diesels. Get one of those old 4BT diesels like they use in older box trucks, and that thing will run until the end of the world. Hardly any electronics at all (less than the 4.0), and built like a tank (also very heavy).
The new diesels have crap tons of emissions on them and electronics galore. My buddy is a veteran diesel mechanic, and he always goes on-and-on about how much he hates the new diesel engines in terms of reliability and maintenance (ease of working on them). They've gotten to be the same as a modern gasoline engine. Sure, they're more efficient than the older diesels, but with that comes a slew of electronics, sensors, and tons of other junk.
So it's a toss up... Do you want something simple to work on, built like a tank, and very stout? If so, I'd probably say stick with your 4.0 or just get an older 4BT diesel.
However, if you don't mind the complexities that come with a newer diesel, then go for it. If the 4.0 can last engine 600k plus miles without touching the internals, I suspect the same can be said for any modern engine.
Engines have gotten to the point where you don't need to worry about internals for a long, long, long time. That's never what fails, it's always electronics, sensors, cooling systems, or seals, pretty much every time.