Maemo/N900 or Sailfish ? On Sailfish there should hopefully be something to test as soon as the Merkator app/daemon by Basil is released as for initial support modRana just needs to add a new layer pointing to the localhost tile server.

As for N900 there and generally outside of Sailfish - it will depend how portable Basils solution is it might be also possible to use it outside of Sailfish or a corss platform modRana-based solution would be needed. But such a solution is still just in the (even though quite detailed) design phase with not much usable code. Also I'll really finally try out your python-mapnik port soon (TM), I promise!