I seem to recall some OMGNOOOOO speculation about similar capability being usable to snatch content to which one had no particular right to make a permanent public archive (I think someone said "Yeah, and think about all the people who'd just feed the sports page into their journal" when this came up on LJ) so when the remote site offered the ability to authenticate with OpenID or OAuth, that might be a good plan.

If it does happen, links to the source should be automatically included; if someone wants to remove them, they could edit it manually. (My journal was embedded on someone's ad impressions site without my permission and without linkbacks, which led to me ragefacing and cutting my LJ syndication down to links-only.)