Add no sooner than verbiage

Author: emmatyping

peps/pep-0784.rst

@@ -233,7 +233,8 @@ Backwards Compatibility
 
 This PEP introduces no backwards incompatible changes. There are currently no
 plans to deprecate or remove the existing compression modules. Any deprecation
-or removal of the existing modules is left to a future decision.
+or removal of the existing modules is left to a future decision but will occur
+no sooner than 5 years from the acceptance of this PEP.
 
 
 Security Implications