Hi,
Just pushed support for percolation on the index and bulk operations. More details with samples here: https://github.com/elasticsearch/elasticsearch/issues/issue/636.
This can be the basis for an event based systems, where after an index operation, the matches can then be distributed to interested parties.
Events being sent directly from ES for percolated index operations (with rabbitmq, webhooks, or something similar) to registered interested parties is down the road (not sure for 0.15).
-shay.banon