I had a 2001 Dodge with the Cummins engine. Cylinders 5 and 6 were under the cowl but no one ever pulled the cab off to work on those trucks. The inline cylinder configuration leaves a lot more room in the engine compartment to work than a V8 does.
Ford was working on a deal with International for a smaller version of the Powerstroke to put in the F-150. Then came the first generation 6.0 with all it's fuel system problems and Ford backed out of the deal. Apparently it was International or nothing at that time for Ford diesels. GM used to offer the diesel in their 1/2 ton trucks, all the way into the 90s I believe. IIRC, the introduction of the Duramax ended diesel powered 1/2 ton trucks and Suburbans for GM. GM actually used a slightly different version of the 6.2 and 6.5 in the 1/2 tons than in the 3/4 tons or higher. And it worked well. I had a friend with a full size blazer with the 6.2 that got almost 25 mpg.
The Cummins in a Nissan would probably draw a lot of business to Nissan like Cummins draws business to Dodge. Personally I'd like to see a diesel Toyota Tundra or even a Tacoma. A diesel Tacoma would be a great commuter vehicle with capability to do some light work.