I wonder if that scenario might be of interest (if it's not implemented yet):
no comments in WP, but allow comments in LJ and import them to WP?
LJ has now option to comment with facebook/twitter/lj/google/vkontakte/openid/...
so that might be usefull if someone like me does not want to set up all these commenting options with extra plugins, but still want to keep my blog fresh with new comments from LJ?
p/s/ do that only for posts which are shared