These Ducato vans are the popular 'platform' for camper vans in Europe, due to the low floor. Most of the conversions have worked out the hard problems and been 'debugged' with customer feedback. The swivel seats come already done properly with no hammer needed. The various tanks for various fluids are worked out. Spares can be bought, plus you get something better than really heavy plywood carpentry - actual cabinet-making.
We all have our own dreams, however, from my experience of living with a camper-van mad family, second hand is good. I would not go for brand new van that depreciates and custom prototype carpentry when people vastly more experienced than me have done it all before hundreds of times over.
It looks like the Ducato is not available in the U.S. Presumably the author could fly to Europe, purchase one, and ship it back for less expense and labor. But I think part of his venture was to have some measure of self-reliance / DIY. "How I bought a great van from Europe and now I live in it" doesn't have the same novelty and escape-from-society appeal.
- the T6 is smaller than the Sprinter.
- OEM. You'd need to go aftermarker for a pop-top. And as as awesome as it is to DIY, not everyone has the time/skills for a conversion.
- Volkswagen cult appeal. You can't deny there's a demand for older T2/T3s and Westies. They released the Beetle for nostalgia, they can do the same for the T6.