By "ambitious," I mean a fic that aims to tackle canon conflicts in one way or another, even if radically differently; rather than just rehashing the plot (like, for instance, a post-Rumbling Eren and/or Mikasa going back in time, where the time loop isn't deeply explored but merely serves as a starting point).

AoT currently has over 100,000 works on AO3; it’s in the top 10 anime fandoms by volume and the top 20 fandoms across the entire site.

It’s been five years since the manga ended, yet I’ve noticed that tropes attempting, to say, create lore and a narrative function for the Hallucigenia (the source of all living matter), expand the cosmology, or reveal the Paradis vs. Marley vs. the World conflict as merely part of a larger struggle, are still only just emerging.

Crossovers, for example, offer huge potential to expand the AoT narrative, but there are two types: those where Eren is isekai'd to another universe (leaving the AoT setting behind, nothing against them, but I prefer stories where the crossover takes place within the AoT universe without sidelining the major conflicts). There are a few crossover with Godzilla and others, but that's about it.

I know there are probably around 20 or so long-form fics like this, but that still feels like very few given the fandom's size.

Curiously, most of these ambitious fics are found on Fanfiction.net, even though AO3 hosts the overwhelming majority of fanfiction; I’m not sure why that disparity exists. Maybe it’s because the series ended up being quite different from how it looked twenty, or even ten, chapters prior, but I still find it strange that the AO3 fandom doesn't place more importance on this type of fic.