The Metadata Server is no longer a service the Scene7 supports. It was deprecated 31-Oct-2016 with notice to all companies that had used the service in the month prior.
There are no plans to replace it with general search service. Metadata associated with an image User Defined metadata is available through ImageServer "req=userdata" and format can be requested in a JSON format. But this would not support general search capabilities. It is dependent you making the request for a specific asset by ID.