Lately I've been thinking about how I'd like to see more plot threads involving player characters versus NPCs. Threads primarily involving combat with Grimm are easy to write and can be fun, but I feel that it doesn't usually lend itself to interesting development outside of, say, a character's combat skill. PvP allows for a bit more variety but it isn't too often that we see player characters with very strongly opposing ideologies pitted against each other. Criminals, mercenaries and killers are just a few examples of character types that always act as a good foil for a Huntsman-in-training, but they are harder to come by. Personally, I find that these types of conflict can be very engaging for both the reader and the writer. One has to think deeper about how their character will respond to this type of confrontation, as opposed to them battling monsters or sparring. This is especially the case when NPCs are built up over time so that they feel relatable, alive, instead of just another vague threat that must be defeated at once and then discarded.
This isn't to say that threads with these type of interactions never happen. There are a lot of past examples to point to, some rather recent ones at that, but I do know that these types of stories are something that I myself would like to get my characters involved in more often.
On a different note, I think it'd be interesting to see the idea of a typical Grimm battle thread turned on its head. Rather than taking down a horde of beasts or hunting a big strong monster, it could be interesting to see characters up against something that they can't simply stab to death or blow up with enough artillery. An unfathomably powerful enemy involving horror elements, shrouded by a sense of uncertainty and mystery, a creature of Grimm that is challenging to simply survive; I think there's a lot of untapped potential in that sort of thing.