Clarify purpose vs role extension on CIP-1852

Author: KtorZ

Diff for: CIP-1852/CIP-1852.md

@@ -58,6 +58,12 @@ Here, `chain` can be the following
 
 Wallets **MUST** implement this new scheme using the master node derivation algorithm from Icarus with sequential addressing (see [CIP3](../CIP-0003) for more information)
 
+### Future extensions
+
+As a general pattern, new wallet schemes should use a different purpose if they intend to piggy-back on the same structure but for a different use-case (see for instance [CIP-1854](https://cips.cardano.org/cips/cip1854)). 
+
+The `chain` can however be extending with new roles so long as they have no overlapping semantic with existing roles. If they do, then they likely fall into the first category of extension and would better be done via a new purpose. 
+
 ## Copyright
 
 This CIP is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/legalcode)