We have a Sprinter 4x4 high-roof on order through SMB, and we're doing a shower. It'll be their smallest shower with a porta potty. We'll just slide the potty into the hallway to shower, or do a seated shower with the potty inside. We just toured the Fresno facility, and it's plenty big for a standup shower. For 2 people, I think there is plenty of room in the sprinter for it. Our layout will have the shower directly behind the driver, followed the the fridge mounted in a low-top cabinet. We'll have a width-wise dinette in the rear so we can maintain a walk-through layout. Sink, stove, and some low-top cabinets on the passenger side. Two rear windows, sliding door window, and a small window in the bathroom.
We'll be doing a lot of winter camping and neither of us were too stoked about taking a grump when it's 10 degrees outside. We climb, bike, backpack, etc and a big part of going with a Sprinter high-roof was being able to take a shower once back in camp (regardless of the season or temp), but still maintaining an airy layout and not feeling cramped.
We were pretty set on getting a well-equipped teardrop for 25K. Our Cayenne Turbo is more capable offroad than the sprinter, and has power to spare for the towing duties. But, there is just no good way of making a teardrop a 4-season unit. The Sprinter, however, is perfect. Just capable enough offroad, just enough interior space that we have *all* the conveniences of home, and the price is right.
You do lose a lot of space with it, but we'll have a full roof rack to store our gear that doesn't need to be inside. The space between the driver seat and bathroom (bathroom will be set rewards a few inches) will be covered in rubber with the cargo tracks everywhere. That will be our space for hanging gear and storing our skis. Space will be a premium on the inside. But, the bathroom/shower sold us on it.
So, if it's something important to you, I say go for it. I'll agree that I'm surprised that more people don't do it. But, I think the Sprinter layout is more conducive to a shower given the interior space than a Ford-based SMB (most of those are pop tops).