Yes, and another example is [sender resolution](http://doc.akka.io/docs/akka/2.3-M1/scala/persistence.html#sender-resolution) in channels. The [current implementation](https://github.com/akka/akka/blob/releasing-2.3-M1/akka-persistence/src/main/scala/akka/persistence/Channel.scala#L92) still uses a stash-based approach where a replacement with a queue actor (or whatever on-demand stream) would make sense. 

In case of channels, a performance issue will only show up if sender resolution is enabled by the application and replayed messages pass a channel (which is the case for non-confirmed messages after a JVM crash, for example). It is not needed for *normal* channel operation but may be a significant problem if a application recovers from a crash under high load.

I'll also need on-demand streams for reliable channels (which I'm starting to work on now) and will try to make the command queue actor a common (akka-persistence) utility that can be reused across processors and channels.