If one could sign in with OpenID to verify control of remote account, and then choose to save this publicly, access-locked, privately, or not at all, and then fetch one's publicly available FOAF (friends data) file from LJ, and then go through that and see:

a) if anyone listed in that file has a publicly verified DW account, list them and their relationship to you on LJ.
b) if anyone listed in that file has indicated that they'd like to show their account to verified LJ-friends, list them as well.
c) also un-authenticated people, with their relationship & the fact that they have listed but not verified, let you make up your own mind
d) ask "Would you like to send your DW username to users on your LiveJournal friends list who have DW accounts and who have enabled notifications for this?" and if there is anyone who has privately verified and has that notification turned on, send a message containing the LJ username and the DW username.

Allow access/subscribe by tickybox to the users listed from A, B, and C
Have a page where one can return at any time and see any & all listed / authenticated (and public or permission-granted) users from one's LJ FOAF who may have shown up in the interim. Refresh as it is accessed.

Please, anyone and everyone, come pick holes in this!