In the US Mercedes Sprinter vans are used exclusively by very affluent people so it doesnt dilute the brand there.

I think that's true as a personal vehicle. But you'll see them driving around with ladders, pipes, etc. on them as direct competitors to the Ford E-Series. You definitely don't see the Ford vans turned into luxury RVs though!

No idea how popular they are, but they certainly exist.

https://leisurevans.com/wonder/chassis/

And also lots of the existing Amazon van fleet.