Now that the Lionhead is gone, the future of the series is probably going to be quiet for the next few years until they eventually decide to revive it and change everything.
If you are holding out for a new game, it might not happen. A HD remaster is a possibility but for the moment at least, there is nothing on the way. For those who are fans of the series, here are some games like Fable that might be of interest.
The Elder Scrolls V: Skyrim
Skyrim is probably one of the bigger RPGs that is somewhat lighthearted like Fable is. The visual style is a lot different, but I don't think there are any RPGs that have the same visual style as Fable. The Elder Scrolls games in general are probably a good place to go. Skyrim and Oblivion are both good games with fun quests and since they have been out a while, you can pick both of these up fairly cheap now.