I recently used React + Bacon + Immutable in a small project and I haven't come across any issues yet. I haven't seen any larger-scale examples yet, but this blog post[0] was interesting and has links at the bottom to implementations of todomvc and the flux-chat example.
Hopefully you'll see a blog post from me on this in the coming weeks =)
I'm a little worried about finding a good answer to the Flux Dispatcher's elegant `waitFor`, but I have a few ideas that I think could handle that well. I'm also worried about "stream spaghetti", especially having streams defined outside of a central `Actions.js`. I'm not yet sure how to elegantly handle server-syncing, though again, I have a few ideas (and Marty seems to provide some too). Lastly, I don't know the performance characteristics of Bacon or RxJS.
[0] http://blog.hertzen.com/post/102991359167/flux-inspired-reac...