Technically you only have to adjust the size of the inlet and handle the rest in software. Since the paper would be comming down vertically, you can do mechanical centering akin to that used in industrial processes.
I like the idea, but doing so still adds a great deal of complexity to a supposedly simple design and adds a large amount to the size of the printer if one accounts for the use of legal paper.
While I wouldn't mind settling on a standard paper size, the design still leaves a great deal to be desired. It appears to be more of a gimmick than anything.