Correct me if I'm wrong, but by "friends-only" I assume they mean people who have joined your fireteam rather than people in your OS-level friends list. It's possible to set your fireteam to open, which allows anyone to group with you by highlighting your character and choosing the "Join Fireteam" option that pops up.
So yeah, that would make it technically possible to attempt with randoms, and I'm sure players will decide on an informal "stand here with an open fireteam for raids" spot in the Tower relatively quickly. Some sort of LFG status that sets you fireteam to open and puts a "JOIN ME!" icon above your nameplate would be better, though.