adding cross site capability for site x's content island y, would be possible, with a mod.
i've done this for my blog (bleeding edge, just for kicks one), to pull in content from various ubbt sites (all diff domains).
if you ask over at ubbdev, it might work out for you. i think i used SOAP, but would have to re-visit. might have been xml-rpc instead, which is even simpler.. bleh, can't remember
you may want to think about json-rpc as a simpler mechanism too. that gives you a 2-way (if you could dream up a why you'd need it)
