There are a few issues with how our file/image handling works that make handling remote files a bit harder than it needs to be.
Some things don't work consistently over InstantCommons because a local MediaHandler class is used that doesn't understand the remote data, and the whole FileRepo architecture is pretty awkward for actually storing "local" files outside of the filesystem (eg the Extension:SwiftMedia backend has to jump through a lot of hoops).
I've started collecting some notes for an RFC on the wiki:
https://www.mediawiki.org/wiki/Requests_for_comment/Refactor_on_File-FileRep...
There's not a lot of specific work targets in there yet, as we'll want some more data from the folks working on the alternate backends as well as the frontend issues which are mostly what I've written on.
But I would like to see if we can avoid having to have a local MediaHandler that's compatible with a remotely-hosted file. As long as the necessary metadata can be exposed, and any rendering can be encapsulated as a thumbnail or an iframe, client sites *should* be able to render anything we can push out from Commons without any special support on their end.
-- brion