What about making a kind of reactive thing that keeps data we got somewhere from aggregated maps that are essentially made of subscriptions and calculations based on said data, just like in "Out of the Tar Pit" paper?

You could. I think that it’s what re-frame does.

What about storing data in datascript instead of maps, like re-posh does? It's a step away from the principle of using mostly generic data structures, but this allows to herd data without schema for a while, when it's not clear what exactly would work

Someone on reddit mentioned Fulcro, which recalculates derived data. That's probably what I'm looking for. To me using just maps is seemingly easy, but it gets much harder quite soon.