DC wanted to do movies of superman dying and returning as well as some other superman movies but they all fell through due to different ideas, superman 4, and batman and robin sucking.
http://en.wikipedia.org/wiki/Superman_Movie_Series
I don't think they ever had serious plans to connect the separate movies into a Justice League movie. Nolan publicly expressed his doubts of Superman existing in his Batman universe. After the Justice League: Mortal fell through there were only promises of solos in development.