So functionally speaking, at this point what is the difference between this "bus" and a diesel RV?
E.g. aside from probably getting it cheaper for the end-product, is there some advantage to the bus vs RV chassis, or drivetrain?
Only some Diesel RV are built on a bus chassis.. most are not..
there a few things I have noticed.. the bus chassis was built for the road so they ride smoother and better on long trips..
EX: when I go over a bridge I get maybe 1 little bump and then bus sits level and rides smooth, other RV's hit bridge and bounce a few times before they level out.
buses were made to carry anywhere from 45 people up to 65 people.. so if you have the factory A/C or heat from the bus it will freeze you or boil you depending on time of the year and weather.
my bus states 30 year or 3,000,000 miles before I should see issues with bus body or frame..
the downfall is I have to make my bus nice, RV's come nice

there are a ton of other things.. but the gist of it for me.. was I could get myself into a Large RV that was mostly complete for cheap.. I could not find any Diesel RV's that even came close for the same price.
but did mount the seat on the passenger side so the wife or any passengers will be very happy

