PEP 667: Incorporate feedback (#3730)

Author: markshannon

peps/pep-0667.rst

@@ -160,7 +160,9 @@ The following C-API functions will be deprecated, as they return borrowed refere
    PyEval_GetGlobals()
    PyEval_GetBuiltins()
 
-They will be removed in 3.15.
+They will be removed in 3.15 at the earliest, and 3.18 at the latest.
+The exact version of removal will depend on the cost of continuing to
+support these functions.
 
 The following functions should be used instead::
 
@@ -179,7 +181,7 @@ The following three functions will become no-ops, and will be deprecated::
     PyFrame_FastToLocals()
     PyFrame_LocalsToFast()
 
-They will be removed in 3.15.
+They may be removed in the future, but no earlier than 3.18.
 
 Behavior of f_locals for optimized functions
 --------------------------------------------