I think in the end, what you and anastigmatfic wrote about Peter and Mary could possibly work in the Last Battle AU fic/commentfic but it just seems out of character for them in the normal TSG universe. :-)

(Btw, this was the perfect thing to get my head out of "Doctor Who". I needed something to drag me back into Narnia and all this discussion about Peter, Mary and Susan was the thing to do it.)