Thanks! This is really intersesting and insightful. I'd definitely read the blog-post if you get round to writing it!
- isolated systems evolve through unitary time evolution; and
- coupled systems evolve through an application of the measurement process.
Decoherence is an attempt to reconcile these two processes, but it's not clear that it works for systems with spatialy seperated entagled states. However, it all works out if you define a theory with emergent locality.