Is there an advantage of getting so far ahead of implementations? It seems like it would be more difficult to incorporate lessons.

When AMD introduces a new Desktop CPU series IIRC they claim the next generation design is (almost) finished (including layout?) and they start with the next-next-gen design. And I'm also asking the same question. But more than a half a year before the CPU becomes available to the public it is already being tested by partners (mainboard manufacturers and ?).