Right now I don't know what other database I could use, because I found no other solution that supports this kind of functionality, especially in a distributed setting.
I agree with most of your analysis and I think that the most important part is about "worse is better": many of your potential customers won't understand or won't care about correctness or consistency.
That said, I really like RethinkDB (oh, it does have its warts, but overall it's great), I'm very thankful for it, and I hope it will continue as an open-source project.
The only other option is to put something in front of a DB like FeathersJS, or deepstream.io
RethinkDB is a breath of fresh air and I really hope the community will be able to keep it alive.
It is more of an object model that a straight up JSON store, but it has some of the best notification features I have tried. You can observe both object and query results in realtime, and since the dataset is replicated to you it has zero-latency local access.
They used to only support mobile, but now they also have a node.js version for server side use.
In my opinion Realms observability is light years ahead of all the other offerings out there.
Have you looked at Datomic? It's not free but I think it provides the functionality you are looking for.
But "$5000 per Year per System" is outside of my price range for the foreseeable future.