I want each LiveJournal installation to be an identity server, and other sites can selectively get your identity info, if you give them permission to have it (and for how long).
Along with namespace separation, this will let LiveJournal and DeadJournal users roam between the sites, leaving comments on each other's stuff. And hell, we might even support each other's userinfo head icons, so when a DeadJournal person comments on your post, you see a skull icon. But that's quite a ways off.
hozed is interested in all this too, and brought up a more global effort at this:
We might just want to support that instead. (I haven't finished reading about it, but it looks thorough.)