Anything changed on thoughts of 7z support yet? 7-Zip is free and open source, and often has better compression than rar, so outside of some janky technical reasons, it seems like a bit of a strange choice to allow WinRAR but not 7-Zip...
It's especially good when bundling different older versions of the same character, while WinRAR compresses each sprite/sound/etc file separately, 7-Zip seems to see the duplicate data and merge it, often reducing the size as though there was only one copy in there. I download a lot of stuff so I've had a lot of test cases, and most of the time 7z gives the better compression ratio (and zip is pretty badly compressed lol)