Basho is implementing a much better search option based on distributed Solr (instead of relying on something in-house), due out this year with the 2.0 release. It's available for testing today.
"Based on distributed Solr" might be an over simplification. It uses Solr as its indexing engine, but really, that engine could be any single-node indexer... including single ES nodes. Basically, Yokozuna adds real grownup distributed systems computer science to the OSS distributed search space. http://docs.basho.com/riak/2.0.0beta1/dev/advanced/search/
I have briefly checked the Riak yokozuna project, and it really looks great. Nevertheless, I'd prefer to have the data storage cluster and the search cluster to be separated (and I really like ElasticSearch too).
Edit: I shall add that the most interesting search problems are the ones where you need to join separate data sources, and in such cases it is not really the question of what kind of search solution you are using, rather what kind of async queue and data update you have. So the separated cluster is really about having a distributed queue between the 'data-master' and the 'search-master'.
I am not sure what difference it makes to have Riak or Riak CS for data storage, in the context of having a separate search cluster. Would you elaborate?
Yokozuna and CS (or plain Riak) use different backend configurations[0,1]. So beyond having physically distinct clusters, you'd get to have purpose optimized storage, but with a common management regime.
