I thought the Narnia series was actually good, and was looking forward to the next installment. In my own opinion I thought what Disney is at fault for their "poor sales" for the franchise in their mind. The movie opened in the middle of May at the start of the summer blockbuster season. Personally I thought this movie could have been released in the fall or winter with a better result in sales. When the movie had to go up against Iron Man, Indiana Jones and the Kingdom of the Crystal Skull and the best movie of them all The Dark Knight, it wasn't going to perform as well. I know there were other factors that this decision was based off of but if they were to just go off of sales alone well there ya go.
But as far as making it an attraction in DCA I would have passed. I did the Narnia walkthrough in Disney World this last summer and didn't find it to be all that great. So it would have been fine to keep the franchise just not do anything in the park about it.