As example: 

Interface is defined in the template, i.e. 

pcfSliceProfileConfig:
      type: topology.nodes.ctc.entityCollection
      properties:
        ..
      interfaces:
        Standard:
          create:
            implementation: 'camunda/so-sbi-workflow'            
          delete:
            implementation: 'camunda/so-sbi-workflow'

In SDC , on the entityCollection VFC , if:

• there are no interfaces defined 
• or if interfaces are defined but they do not have implementation details. * This is what we could expect to see often, as we dont want implementation details at the VFC level , only at service level

then importing this template will throw a generic error message, and the import will continue, albeit the service will be not usable, as missing interface section / requirements are missing etc. 

If no interfaces exist on the VFC , it will not recreate them per the template

Expected behavior for above:

• No interfaces defined on the VFC
  • SDC should create the basic interface operations on the VFC  - Create / Delete  etc - with no implementation details
  • Add the implementations to the interface on the Service side
• If interfaces are defined on the VFC with no implementation details defined
  • SDC should import successfully and add the implementation details to the interface on the Service side