.RAR is the standard (which you already noted), even though most tech savvy users will know what to do with .7z files there's still a chance some might not. We've also got not tech savvy users whose heads would explode at the very instant of noticing an unknown file (they would most likely have the ability to hide known filetypes in Explorer turned on)
Also I do think most AVs are capable of scanning through .7z encoding...
Another option would be to protect the files with a password, but again this would lead to inconvenience for our users (users, as all humans, who generally do not like to read anything at all nor follow instructions(even if these include a password)

).
So, my take on it: not gonna happen

(Our friendly neighborhood admin (Lite) could of course overrule me, but then again: most likely not gonna happen