For general embedding, I think Commons needs to be exposing better metadata (in the form of opengraph or whatever) and then it’d work with Onebox and lots of other systems (like WordPress’ embeds, at Diff).
I tried making a WordPress plugin (embed-wikimedia) for doing this a few years ago, but ultimately it feels like it’d be better to follow existing standards of metadata interchange than create separate fixes for each system that wants to embed this content.