I like that only permitting writes to other cores' memory simplifies the design. If you want to read, you have to write a request to that core by storing the request in a place it will look, and tell it where to put the answer. And, all the cores heve to check for such requests.

It is kind of surprising that that is acceptable. I suppose the usual case is that each core already knows what its neigbors will want to see, and sends those values before each neighbor needs them.