> many minivans no longer meet one of the original design criteria of the first minivan: the ability to carry a 4x8 sheet of plywood.

I don't know about "most". Current Honda[0], Toyota[1], and Chrysler[2] vans are still up to the task.

[0] https://www.middletownhonda.com/honda-odyssey-cargo/

[1] https://www.toyoland.com/trucks/sienna.html

[2] https://www.boston.com/cars/news-and-reviews/2016/04/02/2017...