Joining a private space that's set up for steganography, or facilitating such a space either by self hosting or by logging in somewhere as an administrator, is sort of at odds with the nothing-to-see-here approach that steganography takes. An adversary that has compromised one message can then use whatever metadata is intrinsic to that space to suss out which other plaintexts might contain a secret, and which other humans might be exchanging secrets in that place.

The ideal hiding space would be visible to the public, and indistinguishable from a mountain of other material that's visible to the public--especially if they don't have to log in to see it. That way if a message is found, the search for co-conspirators doesn't narrow at all.