What a creative topic! Yes, as noted, the series has included great literary figures, so why not Lewis? That would be a fantastic episode and should be sugggested to the producer. Perhaps a link to this thread?
Maybe the Doctor needs the help of the Inklings and stops in at the pub for one of their readings. He would fit right in! He could hear some of the
Lord of the Rings or
The Lion, The Witch, and The Wardrobe being read to the group. In fact, the Doctor would love it so much, he would have a hard time keeping his mind on his mission. There's a scholar and a philosopher in him to be sure. Lewis, Tolkien, Williams, and the others must help Dr. Who figure out how to vanquish some menacing evil from another world wreaking havoc on Oxford with their language, mythological, and literary expertise. It could also include little details from their works like a broken sword, a healing liquid, etc. . . .
And it could end with Dr. Who venturing into a wardrobe with a huge grin on his face.
Member of the 2456317 Club. "How will you know? . . . Odd things they say--even their looks--will let the secret out. Keep your eyes open. Bless me, what do they teach them at these schools?" - Professor Kirke in LWW