You can use much of the J and the A during the SSG stage that then delivers the M to the user. And very user-specific and/or dynamic things will have to remain

You can use much of the J and the A during the SSG stage that then delivers the M to the user. And very user-specific and/or dynamic things will have to remain some sort of generated shell and the content fetched on the client anyway. JAM has other problems. I don't think that's one.