How would a lawsuit against him work in a case like this?
The domain name is identical or confusingly similar to a trademark or service mark
in which the complainant has rights;
The registrant does not have any rights or legitimate interests in the domain name; and
The domain name has been registered and the domain name is being used in "bad faith".
Libera could probably get the domain transferred into their control. Especially if they set up their trademarks right as another comment mentioned.https://en.wikipedia.org/wiki/Uniform_Domain-Name_Dispute-Re...
I think the real question is if they bothered to register it.
Freenode is using the Libera brand to advertise their services by registering a Libera branded domain — purposefully to re-route customers looking for Libera properties.
Since Freenode is in the same industry and provides the same services, and is using the Libera brand to direct to their services, it seems particularly egregious.