In my personal tasks app, I got really hierarchical with piles containing cards and decks containing piles. Of course, you might want to see cards together that aren't in the same pile or deck without moving them permanently, so I started building "views" that let you group cards without moving them.
Then, I realized that means decks-and-piles concepts are actually too inflexible. I looked back at "Field"
, my attempt at this kind of problem last year, and I think that something like that, using the architecture I have currently might be the way to go. Not so much the gravity stuff, which was tricky to understand, but I like the approach of just letting users physically put things where they want like Mural does (and providing tools to make it easier than manually dragging every single thing). And perhaps as many layouts of the same cards as the user wants.
On the other hand, I kind of want to just stop doing this entirely, but I might just be tired at the moment.