The design used on the WDW Monorail is owned by Alstom, it's propriatary. Not to mention nobody has made a monorail that would fit the beam size Disney uses in decades, because it's not the standard everyone adopted. In addition we're talking 12 trains here. No big manufacturer is going to swap out a whole production line for a totally bespoke design for such a small order without it being worth their while.
So yeah, any monorails being made will be totally bespoke with very little being taken from an existing design. This doesn't even take into account the fact that Disneys monorails have to be a very specific shape and size to fit through the contemporary, and no, changing the contemporary isn't a simple thing either due to it being part of the fabric of the building, with structural supports running along either side of that entrance/exit point.
We all want new monorails but its far more costly and complex than you think.