[garbear]

Another thing most cores don't support zip/7z i know we could run uncompressed but it just saves so much space having the files compressed, instead could we get compression support into retroplayer instead of the cores? so if we do run them compressed retroplayer can extract them in a temp folder for playing? i know this might make some games take longer to load but it would be up to the user if they can accept the loading time.

VFS stands for "virtual filesystem", and is how Kodi loads anything not directly a file on the hard drive. This means network drives, and is also how Kodi is able to load files from inside zips. So cores with VFS support can load from zips, whereas those without cannot.

You've touched on a good idea. Caching VFS files on a local drive means that all cores can load from the VFS, even without VFS support. This also means that Kodi could generate a ROM library by caching files from a web server (like internet archive). This is definitely something to look into.