I sort of missed it when I first spotted that something moved in the WS-RM msdn home.
Meet Web Services Reliable Messaging Policy Assertions, or WS-RM Policy: a pretty neat spinoff of the main WS-RM spec, where all the policy elements which survived up to the third revision are gathered.
Oversummarizing everything boils down to one single assertion, wsrm:RMAssertion. The assertion mainly means:

• that you want to use ReliableMessaging (and that's a MUST)
• that after a certain timeout you MAY forget about the sequence
• that your patience is limited, and after a BaseRetransmissionInterval without receiving news about the delivery ofthe message you'd give it another try
• that you may want to temperate your impatience playing with exponential backoff algorithm
• that the destination MAY buffer dued acks until a certain AcknowledgementInterval pass

That will go in the good old WSDL, on the wsdl:binding or wsdl:port, per WS-PolicyAttachment: SequenceRef is gone.