Parallel Worlds is the only noteworthy Zelda hack (in quality, completeness, etc., it even has a 2nd Quest) as far as I know. It's just really really hard. It would be awesome to even see an OoT hack that wasn't just texturesI'm talking OoT and MM. The surface has only been scratched, but yes it's possible. The process is so difficult though that nothing substantial has come of it (as far as I'm aware of).