The main problem with FF (or the lack of it) is the fact that the current joystick/wheel library (PLIB) does not support it. There was discussion about moving the joysticks to SDL, which has been promising FF in SDL1.3 - which still isn't released. There was a patch back ported, however this doesn't appear to work with 2D devices (ie. joysticks).
So overall the FF situation is a bit of a mess. If you'd like to work on it, then that would be great - but we don't expect anything will be done until after the upcoming SD 2.0 release.
Simon.
EDIT: If you want to try SDL1.2 with FF patched in I did a set of '.debs' which you can get here:
http://mungewell.org/Logitech_Wii_Wheel/