One of the issues we had with implementing a SCIM handler was that our client's didn't use the bulk processing. This meant that when they added <insert large number> of people to our system, we'd be hit with a large amount of individual POSTs, and they literally all came together.

In hindsight we could've done many things differently, but the usage of this service is generally very spiky, so hard to scale, but wasteful to have additional servers just idling.