This should return all percolation documents stored in the elasticsearch search cluster:
POST _all/.percolator/_search
It searches for indexes (all indexes you registered) for documents like .percolator.
Basically this is what you described above: "match_all with type filter". Nevertheless, he does it a little differently.
I have not played with this much more than this, but I assume that it will actually allow you to execute a query / filter on percolators if you are looking for a percolator of a certain type.
This is version Elasticearch 1.3.4
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