Fun fact: one of the XState devs did a proof-of-concept showing how to use XState state machines as Redux reducers and integrate the side effects handling as a middleware:
Yeah, if you've got any particular use cases or ideas for how you'd like to use them, please put up a discussion thread in the RTK repo and let's talk!
https://github.com/mattpocock/redux-xstate-poc
We'd like to work together to turn that into a more official integration sometime soon.