Every RV now is center aisle because of the slides but you never see the bathroom on slides wonder why ? must be because of the plumbing, mine has 2 large living and kitchen slides then the bathroom has none then bedroom has 2 slides, I still don't like pocket doors I have 3 in that small area with a large open curved shower
I have seen whole kitchens on slides, so plumbing for those i.e. smaller flexible hoses seem to work, but I would always be concerned that eventually...
Larger sewer hoses would be harder to get a good flexible hose, but someday they probably will, thanks to Nasa. :-) But the kinking and flex ridges could be a problem for anything except for a macerator toilet as I have. My toilet exhaust hose (if that is what you want to call it) is flexible and is only 1-1/4" in diameter so that is probably doable. But I pity the RV Mechanic that will get the job of a busted sewer flex hose in an RV that he has to crawl under to fix, but they probably do this all the time.
Even if I had the money or know-how to put a potty on a slide in a bus conversion, this is probably not something I would do until a better solution for waste comes along.
