Currently, querying a collection can only be done through a GET call (https://www.ibm.com/watson/developercloud/discovery/api/v1/#query-collection). This is an issue when the query parameters (actual natural language query, filters, passages settings, etc.) get very large. The request either gets arbitrarily cropped or is blocked somewhere between the client environment and WDS.
It would be very useful to be able to query WDS using a POST call with a JSON-object body mirroring the current query parameters.