How about content similar to fey or pillar but independent of affinity for the purpose of player teams… this way, you are able to deploy your strongest tank and supports with best damage type units and debuffers in order to either fight against a very strong world boss for ranking purposes and/or clear a weekly trial dungeon for rewards, etc.
Might just be an interesting way to mix it up and not be stuck with undesirable affinities for the units you like to use.
Since poison and radiance would never be together by affinity, it could be really interesting to be able to use ardreth/acilia/garius with a lothair team and have gillian/rose/felosia/aladiah as a support. Obviously would be specific content and not related to the overall season, but could be something customizable on a weekly basis for players to fool around with favorite units.