@vincr: would also be a good option for me. Multiboot of MeeGo/Sailfish and more is possible (see ubiboot readme) and this video: http://www.youtube.com/watch?v=DXk7HkAa1Wc but I also don't know how to set up partitions.

Seems like you must reinstall, but then Harmattan won't be harmed:
http://www.jollatides.com/2013/12/09...n-n9-tutorial/

Does anyone know a way to backup everything? Not just settings, like the backup prog does? Anyone tried backing up all files and just overwrite a fresh flashed N9 with that?