There are no (known) legal barriers to uncompressing a .mobi file, so there is already an alternative to mobihuff that will probably stay around. It is mobi2oeb which is part of libprs500. Note that this does not remove DRM, and unfortunately the .opf file it generates typically does not work with FBReader. I delete the .opf and form a .zip file which then opens on the .html file in FBReader.