There is actually a discussion on the fbreader site about this. They won't include it, because .lit is not an open format. I guess legally it would be acceptable to modify fbreader in such a way that when opening a lit file, it actually uses convertlit in a temporary directory to extract the lit file and then opens the extracted files in fbreader, however the developers seem somehow reluctant to do this. It is a shame, but the view of the developers is acceptable (to me at least).