First off, if you have a washer/dryer unit, either a stackable or combo in a small coach, it's probably taking up valuable room. Our first coach that had the space was a 2005 36' Monaco Diplomat. It had a space for combo unit. I put just about every gadget into that coach, but never had any interest in the combo units. When the coach was new, combo units were relatively new and didn't work all that well. They're much better now.
We have a new 2014 coach that came with the stackable Whirlpools. If I had ordered the coach new, I would have ordered them. My wife has always said she doesn't need a washer/dryer in the coach. I always wanted one. During our initial shakedown trip we were trying everything in the coach. On the last night, my wife threw all of our dirty clothes in the machine and was ecstatic as to how nice it was to have all the clothing done before we got home. I was always sold and now she is too.
Having the washer/dryer is kind of like having kids and grandkids, until you actually have them, you don't realize how wonderful they are. Speaking of kids, we camp with our two daughters, who own their own TT's, and their children (grandkids). On more than a few occasions it would have been handy to have the washer/dryer when one of the kids got sick and soiled their bedding.
Our coach also came with a drawer dishwasher. We had only used a few dishes on the first trip and we just loaded them in the drawer as we used them. On the last evening we rand the dishwasher....it was great and quiet. The next morning we put the dishes away and drove home.