a)
Community have tried to make new OS 'from scratch'. Nemo/Mer... No success yet, but we can count these were basement for Sailfish OS.

b)
Community have tried to keep Maemo and replace outdated core from newer Debian (rebasing). No success yet. Many deep packages e.g. libc and glibc already work.

c)
Community have tried to start from newest Debian and bring Maemo top of that. Hildon is already running, but without GL-drivers it is not usable.

d)
There are several other non-debian distros running on N900. Arch, Gentoo.

e) ... (something?)


I vote for option C. Then Maemo would get much updates (and packages) from Debian and work will be 'only' hardware-related and hildon desktop environment.