DDSXTY14 — Inheritance rule regarding keys is overly restrictive

The Resolution Summary of DDSXTY13-23 states:

Structure types can inherit from other structure types as long as:

• [...]
• The derived type does not define any key fields.
  Is this really what we want to do. Will it break some definition where the "base type" is just being reused as a "header"?

I propose to change the first sentence to

• The derived type does not define any key fields if any of its ancestor types is non nested.

This restores viability for the mentioned use case where the base type(s) are just being used as header(s).
It hinges on the assumption that if all base types are nested then the question of assignability does not arise at the topic level.