I would also love to seem someone finally do the rest of the Narnia books as films!!
I really don't know enough about Lewis to say if he was actually against Islam, though he was very clearly pro-Christianity. (see Screwtape, the Space Trilogy etc and his life in general)
But either they'd have to make the Calormenes look different from their book description or risk a lot of backlash. The books have been done successfully on radio.