Add future directions

3.0-Upgrade.md

@@ -18,3 +18,10 @@ guide](https://guides.rubyonrails.org/caching_with_rails.html#activesupport-cach
 * Removed inline native code, use Ruby 2.3+ support for bsearch instead.
 * The CAS operations previously in 'dalli/cas/client' have been
   integrated into 'dalli/client'.
+
+## Future Directions
+
+The memcached project has deprecated the binary protocol used by Dalli
+in favor of a new `meta/text` protocol that is somewhat human readable.
+
+Dalli 4.0 will move in this direction and require memcached 1.6+.