On the August 18 Telcon (see minutes http://www.w3.org/2002/ws/ra/9/08/2009-08-18.html)
We agreed to a direction re. using Policy on endpoints based  on my  note: http://lists.w3.org/Archives/Public/public-ws-resource-access/2009Aug/0033.html
This note made 2 points:

1. Endpoint policy is contained within the Metadata child of the EPR as recommended by WS-Addressing

<wsa:EndpointReference>
  <wsa:Address>xs:anyURI</wsa:Address>
  <wsa:ReferenceParameters>xs:any*</wsa:ReferenceParameters>
  <wsa:Metadata>
    *( <wsp:Policy ...> ... </wsp:Policy> |
        <wsp:PolicyReference ...> ... </wsp:PolicyReference> )?*
      ...
  </wsa:Metadata>
</wsa:EndpointReference>

2. In WS-RA the use of Policy is primarily to indicate Endpoint capabilities.  To allow domain independent processing, each capability MUST be indicated by a policy assertion with a unique QName i.e. the assertion QName indicates the capability.

Now, we need to apply this direction to MEX to indicate whether MEX is supported and which MEX features are supported.

Clearly, the above points need to be applied to other specs as well.  For example, how RM assertions are attached to the NotifyTo EPR for eventing, but these issues need to be raised independently.