It's come up before, even making its way to an April Fool's changelog in 2024, but it was mentioned again in the official discord. I wanted to collect some of the ideas that people made in there, plus a few suggestions of my own.
Some (Iazin, Eiselle, myself) suggested it could reuse squad, clan, and/or player kephera hive code, at least as a platform to stand on. I am not myself a coder and would imagine it would strongly depend on what those specific codes involve. It was also mentioned that something similar, namely polygamy, has been done in Aetolia. I would imagine that Lusternian polycules, however, tend to be more fluid and dynamic. I would also strongly advise that this probably shouldn't touch Family code - nobody would be officially married into anyone else's family, no children could be adopted by the polycule (except in standard solo and married cases, as current), etc.
All verbs/syntax are non-definite and just examples. Said examples also only include being part of a single polycule, rather than multiple.
SYNTAX: POLYCULE
POLYCULE FORM <person1> <person2> - like it says on the tin, forms a polycule involving the performer of this action, plus 2 other people.
POLYFORM AGREE <person> - as above, but person1 and person2 are agreeing to the polycule. No drive-by polycules, please!
POLYCULE INDUCT <person> - brings a single person into the polycule. May or may not need confirmation from other polycule members.
POLYCULE LEAVE - leave a polycule.
POLYCULE DECLARE <person> <relationship|NONE> - declares a particular person in a polycule to be of a particular relationship level/label. Some suggestions might be 'spouse', 'casual', 'complex', 'steady', or whatever other potential labels desired. Everyone starts without a label and they are not required - if someone wants to clear their relationship they can use NONE instead.
POLYCULE CONFIRM <person> - same as above, but it's the second person confirming the relationship.
POLYCULE LIST - lists all the people in the polycule.
POLYCULE STATUS - states whether or not you are in a polycule and what relationships in that polycule you have declared, if any.
PT/PTALK/POLYTALK - private aether for polycule members. Follows the same general in-character rules as is standard. Communication is, after all, key.
The relations declared within a polycule might be private or might be public to everyone in the polycule, but I imagine it could get messy fast listing everyone's relationships with each other... But, who knows.
I imagine similar incest rules currently involved with marriage might apply, or at least, no parents and children can be in the same polycule, etc. Depends on how easy it is to implement, I suppose, but hopefully it's a situation that wouldn't come up in the first place.
EDIT:
Follows standard non-newbie rules for marriage (30+ levels and 75+ hours).
READLOG POLYCULE - does exactly what you think it does.
POLYCULE FORM might be used by persons who are already married - if one or both parties are already married, perhaps they could just require one additional person, to avoid requiring a dummy test player to form it and then later leave.
POLYCULE REJECT <person> - rejects a person from the polycule. Intended for use against abusive individuals.