It would be nice to have a third option for project visibility, “internal” (similar to e.g. GitLab’s internal visibility) that restricts access to a project to (all) logged-in users.
While not useful on public instances like tree.taiga.io (because there, everybody can create an account, so “internal” ≈ “public”, see also GitLab’s reasoning), I’d find it pretty handy on self-hosted instances that are not open to the public.