doc: Comment about Rust 1.79

Author: a4lg

ffuzzy/src/_docs/planned_changes.md

@@ -39,7 +39,9 @@ Depending on the Rust edition target (we haven't decided yet),
 MSRV on the next major release will be raised to the version specific
 to that edition.
 
-*   Edition 2021 case: at least 1.79 (most likely 1.81)
+*   Edition 2021 case: at least 1.79 (most likely 1.81)  
+    Rust 1.79's associated type bounds feature makes our new trait-based design
+    far more easier.
 *   Edition 2024 case: 1.85 (not released yet)