The new policy says "Primary channels are required to stay open. If a primary channel closes access to its users or is in violation of freenode policies, then it will be closed and forwarded to a topical channel."
So I assume that advertising Libera is not (yet) enough to be taken over. Taking over channels that declare themselves closed (and redirecting them to an unofficial channel about the same topic) seems reasonable, tbh.
Channels that hadn't even moved were taken over, such as #elixir-lang. They only had a mention "Also see <channel> on <network-that-shan't-be-named>" in the topic. Well, they have moved now.
So I assume that advertising Libera is not (yet) enough to be taken over. Taking over channels that declare themselves closed (and redirecting them to an unofficial channel about the same topic) seems reasonable, tbh.