Continuing the discussion from Product Vision Flow / Neos:
So this is an idea for a decoupled architecture with two exemplary scenarios. The idea here is to create boundaries around parts of the system that can work in a coherent way and can be more isolated from the rest. Another approach is to use something like an onion layer around lower-level components like the content repository and (at a later point) connect that with a content integration framework for external content source while the exposed API can be kept at a higher level.
The 4 main pieces I see so far are the Content Store, Rendering Engine, Content Delivery (speak routing, caching and delivery of web content) and of course the client in form of the JS UI. The client should be completely decoupled from any server rendering, so no augmentation takes places but everything is done via APIs.
This architecture is neither finished nor complete, but should show what the main idea behind my thoughts is.