These days, pretty much anything that can be imagined can be built. Companies that build RV's have enough trouble building popular RV's that enough people "want" let alone generating excess inventory of those that "don't" sell well. Manufacturers that have managed to survive for +50 years usually have a pretty good idea of what sells. (what people want) That's what they build. Just because you want something, doesn't mean that enough other people do too and that it warrants designing/building quantities of it.
Enter the custom RV. If you choose, you can have anything you want custom built, then break the mold. Be prepared to pay dearly for it, and, wait for it to arrive. Now you have a one of a kind masterpiece. Every part of it is special, built just for you. Be prepared to deal with that if/when it needs service/repairs.
On the other hand, if you are the kind of person who likes to design/build/service/repair things yourself, I'd say a custom built RV is right up your alley! If not, IMO, make sure your RV budget is well padded.
Chum lee