"Also if you have a D1 only world how are you going to decide who gets what team? First come first serve basis? Yep, that's how all worlds filled previously Lottery? Only start a couple coaches at the worst teams and then cycle through when they move up?"
historical perspective - starting in DIII means that the choice of school doesnt matter much - when worlds are new, the rosters are close, the schools all have the same prestige. There are some arguments that some locations are better for recruiting for various reasons, but not much difference.
No world has been DI only. how would you fill up a DI only world - first come first serve? VERY different from prior worlds if the choices are DI so that being first gets you Carolina or Duke or whatever? or open only the lowest rung of DI? or something else?