It might be possible to manage custom views from Lua in the future. At least for viewing this should work. Updating is more complicated.
I was thinking about a way of implementing VFS, which might not even be too complicated, but the great thing about FUSE is that it works in any application you can run from Vifm passing it paths from a FUSE mount. You can't do this with internal VFS, because it's not visible from the outside and things won't work in weird ways (even quickview will break unless files are automatically extracted before viewing, which is not great).