[WIP] Abstract completeness (extensibility point)

| Q                    | A
| -------------------- | ---
| Bug fix?             | N
| New feature?         | Y (extensibility point)
| BC breaks?           | N
| CI currently passes? | ?
| Tests pass?          | ?
| Scenarios pass?      | ?
| Checkstyle issues?   | ?
| Changelog updated?   | Y
| Fixed tickets        | PIM-2662 (partially)
| Doc PR               |