Creating an exclusive journal or conference seems like it could actually hurt building the AI risk research community, by isolating AI risk researchers from researchers in related disciplines. Having a journal or conference devoted to your topic seems like a consequence of having a large number of researchers devoted to your topic, not a cause of it. (And it might be worth avoiding even if there were tons of researchers for the reason I mentioned.)

ETA: I didn't notice that this apparently worked for the AGI conference. Maybe academics are more comfortable presenting to people who are interested in the same topics ?