Update 4.0.1 release notes to mention one more major pain point that Khepri addresses

Author: michaelklishin

release-notes/4.0.1.md

@@ -245,6 +245,30 @@ This section is incomplete and will be expanded as 4.0 approaches its release ca
 
 ### Core Server
 
+#### Bug Fixes
+
+ * A whole category of issues with binding inconsistency are addressed with the stabilization
+   of [Khepri](https://github.com/rabbitmq/khepri), a new [metadata store](https://www.rabbitmq.com/docs/metadata-store) that uses a tree of nested objects instead of multiple tables.
+
+   With Mnesia, the original metadata store, bindings are stored in two tables, one for durable
+   bindings (between durable exchanges and durable queues or streams) and another for semi-durable
+   and transient ones (where either the queue is transient or both the queue and the exchange are).
+
+   When a node was stopped or failed, all non-replicated transient queues on that node were deleted
+   by the remaining cluster peers. Due to high lock contention around these tables with Mnesia, this
+   could take a while. In the case where the restarted (or failed) node came online before all bindings
+   were removed, and/or clients could begin to create new bindings concurrently, the bindings table
+   rows could end up being inconsistent, resulting in obscure "binding not found" errors.
+
+   Khepri avoids this problem entirely by only supporting durable entities and using a very different
+   [tree-based data model](https://github.com/rabbitmq/rabbitmq-server/pull/11225) that makes bindings removal much more efficient and lock contention-free.
+
+   Mnesia users can work around this problem by using [quorum queues](https://www.rabbitmq.com/docs/quorum-queues) or durable classic queues
+   and durable exchanges. Their durable bindings will not be removed when a node stops.
+
+   GitHub issues (discussions): [#11952](https://github.com/rabbitmq/rabbitmq-server/discussions/11952), [#13030](https://github.com/rabbitmq/rabbitmq-server/discussions/13030), [#12927](https://github.com/rabbitmq/rabbitmq-server/discussions/12927), [#12783](https://github.com/rabbitmq/rabbitmq-server/discussions/12783)
+
+
 #### Enhancements
 
  * Efficient sub-linear quorum queue recovery on node startup using checkpoints.