Make it possible to manipulate CustomAttributes for organizational Contacts
Organizational Contacts make it possible to share contacts via Tenant to Tenant. The only decent way to key off source tenant is via adding ExternalDirectoryObjectId to a custom attribute. Please consider adding this to the Graph API. Graph is phenomenal, however, the details really matter when collaborating T2T.
By and large, it just makes sense to have any entity within the system part of the graph as a read/write entity/attribute. Of course, we understand that there are priorities. I think more transparency as to when each entity and attribute will be included in necessary.