In a way a lot of RV's do have a system similar to what you're thinking as quite a few have roof vent units in multiple locations on the roof; many of them are powered vents.
I don't see the solar vents as being as much advantage in a live-aboad bus since folks are there to open windows, vents, doors, etc. For a bus that's not bing actively used they might be nice so that they're working full time even when the bus is unoccupied.
I think a lot of conversions are done based on what we see on manufactured RV's; the prime consideration there (until you get to the high end) is cost and ease of construction (plant efficiency) with relatively unskilled labor. If I were converting a weekend camper I might choose different materials and equipment than I am for converting a 'rolling home' fulltime live-aboard bus. If something breaks on our bus I know who's going to fix it and I know how much stuff is going to be in the way when it needs fixing. I'm doing everything I can up front to minimize the chances of failures and enhance efficiency by using the best materials and components I can. I naturally draw from my boating background.
As has been said here many times; there's no "ONE WAY" to do anything. As long as things are done to maximize safety there are any numbers of ways to "get the job done". Depending on my energy level (and financial level!) my conversion thoughts (for many years now) have run the gamut from bolting down a queen-sized bed in the back, installing the woodstove, throwing in the big floor pillows and installing a curtain around a portable toilet to where I am today with plans to do it once the best way I know how so that it will last the 20 years I need it to. [Of course, as soon as I do something I'll think of a better way to have done it...faster, cheaper, or better looking but that's part of the process!]
I'm learning a lot by hanging out with all these crazy folks (if we weren't crazy we'd just go buy a motorhome and head down to road). I may have a good background in 'systems' like plumbing, electrical, heating, etc, but I'm gaining invaluable knowledge in the areas where I don't have any particlular expertise (or even basic knowledge) like painting the bus, flooring, insulation materials, sound deadening, welding brackets, and more.
I'm having fun and at this stage, that's what it's all about. I don't have any 'end date' for my project and I'm moving at a snail's pace. This is a busy time of year in the boat biz so I don't have much time available and I have a motorcycle I love to ride and the weather has been nice!
We go on vacation every year in the first week of October; there are four adults and four dogs and we head down to Lake Shasta from northwestern Washington. This year I hope to have enough of the basics done that the bus can be our transportation. We have a 1977 Beaver Class C motorhome (on a C30 Chevy chassis with a 454 engine) that we usually travel in and that would still work but I think it would be a blast to take the skoolie instead.