I think the message network misses one of the benefits of this architecture, and that is non-blocking execution at each node. As each node possesses it's own memory for instructions, it only blocks when it is in a read, waiting for another node to write, or when it is in write, waiting for another node to read. Your message network would imply a bus, which wouldn't scale arbitrarily.

Admittedly, a TIS-100 built like this "simulation" would be hard to program without some way of addressing each node.