There is a lot of push vs pull provisioning discussion going on recently. Both models have a place but there is hard and fast rule you should consider. If your solution requires your customers to stand up a web service (SOAP or REST) you are going to be running uphill against a head wind. Customers see public web services as support and security costs they just don’t want to pay.
For most customers it’s far easier to have a system running in a data center that makes that makes web service requests to a provider than it is to stand up a service. Google, for one recognizes this. The Google Apps Directory Sync is often incorrectly cited as a “Pull Provisioning” technology when it is exactly the opposite. The sync software runs on the customer side, reads from the local directory and pushes to the Google Apps Provisioning Web Service.
A proper provisioning standard, regardless if it’s SOAP or REST, should support both push and pull (note that SPML supports both). But I really don’t see the pull model getting much traction for cloud based provisioning. Perhaps it will for provisioning internal applications.