As a long-time Tolkien fan, I find the movies pretty dreadful, and the Hobbit was even worse.
I just can’t imagine how a movie about the man himself would be interesting. His childhood was very difficult, his mother raised him and his brother as a single parent, and it was with a great deal of help from a Catholic Priest (whose name I forget), and I suspect that is why Tolkien was a very strong Catholic his whole life. He fought in WWI, and spent a great deal of time in an infirmary, though those experiences shaped his writing, and his view of warfare (his battles in the mythos are often quite detailed).
But as an adult, he was an Oxford professor, chummed around with other writers and professors, wrote a lot of letters, raised a family, and wrote books and essays. His was not exactly a life filled with adventure, in fact, he didn’t seem to like adventure at all (which probably informs Bilbo’s response to Gandalf at the beginning of The Hobbit).
What I’d love to see is one of the stories from the Silmarillion; perhaps the Turin saga (though it does have unintentional incest). I think those stories, which are less complex in narrative and plot structure than The Lord of the Rings, would translate well.