I think polyamory should be used to make romance subplots even more convoluted, actually. Sure, it could theoretically solve a love triangle- but it could also make things infinitely more chaotic and that's way better.
Some ideas:
- The protagonist thinks they're in a harem anime, but it turns out all the love interests are trying to recruit them into the same polycule but are being bizarrely competitive about who can get the protag to go on a date first.
- Two members of the polycule get married, and nobody is quite sure how to tell the groom that they caught the bride sleeping around. (bonus points if he is actually mad about it, but for stupid reasons.)
- A guy dates a pair of identical twins. Hijinks ensue.
- The members of the polycule all panic because they all bought the same damn thing for Jenny's birthday, and have to come up with a new plan at the last minute.
- A woman has to decide which of her boyfriends she wants to legally marry- because both of them have the most obnoxious families imaginable and they want to make a Thing out of it. (could end with the boyfriends marrying each other for maximum chaos)
- A superhero, desperate to keep their secret identity safe, decides to date the woman of their dreams in both identities, and is struggling to keep it all straight. (bonus points if she knew all along, and was using her supervillain persona to trip them up.)
- A man mistakenly scheduled two dates on the same day, and has to figure out a way to attend them both in rapid succession.
- An evil twin does the classic twin switch, and has to navigate her way around her sister's increasingly confusing love life.
- The most important clue in a murder mystery was the love letter the victim was about to send to "my beloved girlfriend". One of the many girlfriends clearly killed the man, but which?
Political marriages in a society where polyamory was a cultural norm would be a fucking NIGHTMARE <3
On a more serious note: a lot of representation in general either has it as the main plot beat, or are going for a "its so normalized we're not even going to bring it up" route. What I'd like to see more often is it being relevant, but not the focal point of a character or plot.