I have kind of lost where we are on dropping cells v1 code at this point, but it's probably too late in Stein. And technically nova-network won't start unless cells v1 is configured, and we've left the nova-network code in place while CERN is migrating their deployment to neutron*. CERN is running cells v2 since Queens and I think they have just removed this [1] to still run nova-network without cells v1.
There has been no work in Stein to remove nova-network [2] even though we still have a few API related things we can work on removing [3] but that is very low priority. To be clear, CERN only cares about the nova-network service, not the APIs which is why we started removing those in Rocky.
As for cells v1, if we're not going to drop it in Stein, can we at least make incremental progress and drop the cells v1 related docs to further signal the eventual demise and to avoid confusion in the docs about what cells is (v1 vs v2) for newcomers? People can still get the cells v1 in-tree docs on the stable branches (which are being published [4]).
[1] https://github.com/openstack/nova/blob/bff3fd1cd/nova/cmd/network.py#L43 [2] https://blueprints.launchpad.net/nova/+spec/remove-nova-network-stein [3] https://etherpad.openstack.org/p/nova-network-removal-rocky [4] https://docs.openstack.org/nova/queens/user/cells.html#cells-v1
*I think they said there are parts of their deployment that will probably never move off of nova-network, and they will just maintain a fork for that part of the deployment.