Sure I can agree that Tolkien didn’t like the idea of a multiverse but even when he was alive he started building the path for one when he okayed a movie even though he later wrote that whole letter about it and it never came about in his life time.
As to the modern day though the multiverse ship sailed in the 80’s and it’s only gotten further out to sea with every new adaption, the chances of it coming back to port is non existent.