Of these two, I find the second more appealing. The main use cases I have in mind are linking discussions from issues, and in general creating a permanent record of the work we do (our IRC logs got lost, I should have been on the ball to preserve them).

For people who actually want the Zulip experience, I have no problem just asking them to sign up for real. Since we have open signup based on github login, it's a pretty small barrier.