I feel like every time someone sets out to create a F/OSS successor to DF, they end up mired in creating dungeon and world generators and never produce a functional game.
Really, that's what DF is anyhow; they even call it a "story generator" IIRC. Tarn just managed to put enough of a playable game together before getting lost in the details of world generation, and people have stayed engaged enough with it to keep him involved in the project.