No one is really sure what yet, but there is a Clannad project being worked on by AnimeJapan. On their website they have Clannad listed as one of the projects that they are currently working on - which is leading people to believe that something is going on. The debate is almost unanimous that this series could not get a sequel - but a spin off is possible, and maybe even a remaster. The one thing that fans across the board do not want is another Pachinko machine, which would break a lot of hearts at this point.

Link to the AnimeJapan works page: http://www.anime-japan.jp/main/works/
Link to Otakomu article: http://otakomu.jp/archives/469668.html