The reach of Love Live! is so broad, it's hard to imagine they haven't come up with every possible piece of merchandise for the franchise. Even so, fan creators bring out merch and doujinshi regularly online and at fan events.
For better or for worse, though, the rights holders are making it known that Cease & Desist letters are being sent out, and creators of unlicensed merchandise featuring everyone's favorite idols will not be tolerated:
Unfortunately, despite repeated police investigations, Love Live! and Love Live! Sunshine!! merchandise that infringes upon copyright continues to be sold at events and on mail-order sites, as well as as arcade prizes.
We will continue to deal strictly with copyright infringement, and continue our policy to not ignore complaints concerning these malicious actions.
Please take care not to purchase these unlicensed illegal goods. Thank you for continued support of Love Live! and Love Live! Sunshine!!.
It is unclear whether this statement includes fan-created manga at doujin events, but the phrasing certainly makes it sound as though they are adopting a zero-tolerance policy going forward. Some fans believe that the crack-down is because of declining sales after the switch to Aqours. Either way, it seems as though legal action will be pursued quickly going forward.
Kara Dennison is responsible for multiple webcomics, blogs and runs interviews for (Re)Generation Who and PotterVerse, and is half the creative team behind the OEL light novel series Owl's Flower. She blogs at karadennison.com and tweets @RubyCosmos.