Hi, all!
Gary is more familiar with `MessageChannel` architecture (I haven't wrote any one yet ;-)), so he can more effectively lead you, Jon, in this direction.
But want to pay your attention from perspective of Reactor.
Here you *notify* and *subscribe* to the `defaultKey` from `Reactor`, so, if `reactor` is shared one from application context and we're referencing it from different channels we may end up with unexpected results. Isn't it?