Thank you very much for this very insightful post which is among the best discussions of this problem I have seen. It must have taken you a considerable amount of time to put it together.

I do have a couple of points:

1) Drilling a stress relief hole may not provide provide insurance against failure if the failure already started before the hole was drilled. You may be leaving behind micro-fractures that you can not see. Also, I do not see how the interior edge can be deburred. It is still a wise precaution, but does not eliminate the need for frequent inspection.
2) The nature of aluminum is such that with repetitive stress cycles it will ultimately fail, so even if there are no cracks now, there will be.
There are a few sites now that have shown testing of modern stems with cyclical loads and they too will ultimately fail. It is the nature of the metal.
3) Nobody talks much about seatpost failure, but I think the same "rules" apply.

Thanks again for your post.

r