I wondered what happened to .prop() which looked like it had a lot of potential. Looks like that potential was (at least partially?) realized as it evolved into a "stream" library [1], which basically acts like cells in a spreadsheet. This seems like a really useful concept which could be used to create more kinds of UI frameworks than just declarative React style ones.
I just looked over their website for 10 minutes and still can't figure out how it handles more complex nested components with complex state. Is it like Elm and Redux where it has a giant tree and you have to update the root with a bunch of events, creating intermediate adaptor events from the deepest nodes all the way to the top? Does it have anything like React's Contexts? I really like the examples I saw on the landing page, but I would rather like some comparisons of how to do the exact real-world things React can do. Mithril's website did this pretty well. Maybe this is hurting adoption? Or maybe it's just me.
[1]: https://mithril.js.org/stream.html