Issue http://www.w3.org/Bugs/Public/show_bug.cgi?id=6411 was raised a few months ago in order to provide symmetry between the WS-Mex and WS-T specs and was closed.

We now have new evidence in terms of specific requirements that illustrate the importance of this symmetry.  In particular, metadata authoring for a particular endpoint is often performed using specific tooling that may be remote from the actual runtime. The WS-MetadataExchange spec does not allow for the pushing (update) of metadata from the metadata authoring tooling to the location at which the metadata is stored.  

With the specs as they are currently, an endpoint's metadata could be updated by pulling a reference to the individual metadata resource endpoint and then performing a WS-T Put on the metadata resource endpoint.  There are a number of problems with this approach:
1) An endpoint would need to expose itself as a Metadata endpoint AND each of its metadata parts as Metadata Resources (each supporting WS-Transfer Put)
2) It does not allow for updates to multiple pieces of related metadata for an endpoint in a single step.  This may be problematic as the metadata updates might be to different metadata types, but dependent on each other.
3) It requires an extra step (or steps) - one to get the metadata endpoint to which the WST Put will be targeted and one (or more) to perform the actual WST Put(s).  This complicates the solution and affects performance.

This issue is easy to fix (as we are essentially repeating operations based elsewhere) and would enable the Metadata scenarios to be fully covered by the WS-Mex spec, rather than the specs only provide a partial solution to metadata exchange as they do currently.

I appreciate that this is a late change but it is a very important scenario.  I have generated a complete proposal, where possible utilising existing aspects from other specs that we are confident with.

Proposal
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- Add PutMetadata and DeleteMetadata operations to WS-Mex spec (sections 6.3 and 6.4). Note that Metadata creation can be performed by the PutMetadata (there is no need for a create operation).  See comments in the doc for details.
- Update the MetadataExchange Assertion to cater for these new operations (Section 11.1)
- Added faults to support the PutMetadata and DeleteMetadata operations (Section 10) 

Attached is a marked up version showing the proposal.  I have added further explanations as comments within the doc itself.