ACID transactions in a highly available distributed system are hard and often fail in subtle ways when done wrong at the edges. Any implementation will take years to mature in the lab and in actual production usage. This isn’t a knock on the Rethink guys; their product looks pretty awesome and is moving quickly.

For a solution today, MarkLogic is a transactional distributed document database. Cross-document and cross-partition transactions have been a key tenet of the architecture from the beginning (like, 2002 beginning). Take a look at https://developer.marklogic.com/blog/how-marklogic-supports-... for details.

Full disclosure: I’m a Product Manager at MarkLogic.