[brandonbloom]

> that still needs A to talk to D

That should not be the case with promise pipelining. The "Mobile Almost-Code" section of the E page explains this. You mentioned "continuation passing style", which is effectively what promise pipelining does: For the constrained class of continuations that can be serialized as a dataflow graph, pass those along with the message.

Importantly, the system wide constraint is willing participation from each actor, not a shared database. Instead of each actor needing to know how to interact with the shared database, each actor needs to be willing and able to execute these passed continuations.