To run Riak in production you need 5 servers.
Here all you need it S3(scales indefinitely) + 1 elasticache instance.
Here all you need it S3(scales indefinitely) + 1 elasticache instance.
There are things that are missing that are nice about Riak. Mainly libraries, map reduce, 2i, and solr-like text search.
This project definitely interesting for what it is though.