Add bzip2 multicore support via lbzip2 or similar
File roller still only uses one core for compressing and decompressing bzip2 files. Using a tool like lbzip2 (man page) rather than the traditional bzip2 could change this. There is also a tool named pbzip2 which could to the same. Personally, I used lbzip2 a couple of times, when file rollers compressing performance was not enough.
Similar has been suggested here: #5 (comment 291524)