Well then. Despite 7 Zips present age the reality of the matter is what you are actually asking to occur. 7 Zip failed the penetration test with end-users.
Due to the zip or rar or lzh's formats's long histories you are basically asking for anything zipped to be transferred to the newer format. Which does take time, emulator authors don't have time to encode every format into their emulator. Be it free or commerical. It is simply being lost in the shuffle of emulator coding.
7 Zip was once a hot new format for file compression the previous decade. The honeymoon ended and now you see the results. Honeymoons don't last forever sadly.