Sequence diagrams are about my favorites. I made a little REXX tool to generate text diagrams so I can cut & paste them into any kind of doc with no graphics.
We haven't even started to talk about the static relationship between these things, only the dynamic!
Can you imagine an application that requires the opposite direction: pluggable Models under the same View?
We might put the pub-sub code in its own package so that Model and View both depend on Publisher, and neither depends on the other. When is that worth the effort?
What if Word were architected so you could make a new document type that implements a Word model interface so Word could view it without modification?