Thread:Extension talk:Push/Broadening File Support/reply

Most of the code would work perfectly fine with other file types, so it's not that hard to add, but it needs some additional logic, rather then simply adding some file extensions. The JS obtaining the images should obtain all files, but this needs some other API call. In fact I'm not fully sure you can get that info via the core MW API, so you might need to write your own module.

So this is not possible right now, but if someone where to throw some hours of dev time again it, it could definitely be added.