PEP 685: add a tranisition plan

pep-0685.rst

@@ -97,11 +97,11 @@ Tools generating metadata MUST raise an error if a user specified
 two or more extra names which would normalize to the same name.
 Tools generating metadata MUST raise an error if an invalid extra
 name is provided as appropriate for the specified core metadata version.
-If a project's metadata specifies an older core metadata version and the name would be
-invalid with newer core metadata versions,
+If a project's metadata specifies an older core metadata version and
+the name would be invalid with newer core metadata versions,
 tools reading that metadata SHOULD warn the user.
-Tools SHOULD warn users when an invalid extra name is read and SHOULD ignore
-the name to avoid ambiguity.
+Tools SHOULD warn users when an invalid extra name is read and SHOULD
+ignore the name to avoid ambiguity.
 Tools MAY raise an error instead of a warning when reading an
 invalid name, if they so desire.
 
@@ -159,6 +159,22 @@ Finally, if the project ever gains the ability to write out metadata,
 it will also implement this PEP.
 
 
+Transition Plan
+===============
+
+There is a risk that a build tool will produce core metadata
+conforming to version 2.3 and thus this PEP but which is consumed by a
+tool that is unaware of this PEP (if that tool chooses to attempt to
+read a core metadata version it does not directly support).
+In such a case there is a chance that a user may specify an extra
+using an non-normalized name which worked previously but which fails
+now.
+
+As such, consumers of this PEP should be prioritized more than
+producers so that users can be notified that they are specifying extra
+names which are not normalized (and thus may break in the future).
+
+
 Rejected Ideas
 ==============