Deploy previews on GL Pages?

It would be very nice to have a separate subdomain (ci-run-id.username.gitlab.io or branch.username.gitlab.io) as a deploy preview (possibly for authed users only). That doesn’t currently seem possible.

Is the public directory deleted, if new artifacts come in? I would be happy with a solution, where tests put the artifacts in public/.dp/branch-name instead, not overwriting public/something-else.