I always said if you're going to do a Narnia movie franchise, you can't stop before you get to the best ones. Though they botched the plot of Voyage of the Dawn Treader significantly, it seems The Silver Chair - which is to Orpheus what Dawn Treader was to The Odyssey (i.e. a kid-friendly interpretation with new, proprietary characters) - is now in the works.
Thanks to C.S. Lewis' tendency to change up his lead characters from book to book, and age Narnians quickly, the only casting change really necessitated here is the kid who played Eustace in the last film - actor Will Poulter is 20 now. Of the remaining books, only The Last Battle remains problematic in that regard, as it brings together most of the prior protagonists for its allegorical (and most overtly preachy) Book of Revelation. Left after those is The Magician's Nephew, which would be a prequel to all the movies thus far, and The Horse and His Boy, a tangent set during the time depicted in the last moments of The Lion, The Witch and The Wardrobe, in which the original children are adult kings and queens in Narnia. Lewis had an interestingly nonlinear approach to sequels that movie executives today would sternly lecture him for, I'm sure.
The Silver Chair was done once before in live-action for the BBC (above) and starred Tom Baker as Puddleglum, a pessimistic human/amphibian hybrid who serves as a nice cynical counter to the Aslan/Jesus stuff. If done correctly, the new movie will also bring back Tilda Swinton as an evil witch who may or may not be the same one seen in the prior films.
I do wish they'd done these movies all at once, but the unfortunate nature of doing them in semi-chronological order meant the most boring one came second and nearly torpedoed a burgeoning franchise, while the third tried to streamline its episodic nature for a Hollywood three-act structure, and killed a lot of the book's appeal. The Silver Chair, about a journey to the underworld to rescue Prince Caspian's son, should be much more straightforward and suitably cinematic.
Is Narnia as a movie brand dead to you? Was it ever alive? What would it take for you to go see another one?