This is not an entirely new idea, but previous discussion has tended to go in Books and Media or ASB, which tends to attract less of the analytical frame of mine that AH Discussion has, and which this notion demands.
Ultimate AH, as I have named it due to some similarity with Marvel Comics' Ultimate series, consists of:
1) Take an existing published AH story or scenario
2) Find the POD
3) Pose the exact POD now to AH.com
4) What do we think that POD would produce?
Ideally this should be done as dispassionately as possible, not being different for the sake of being different because you dislike the original story. Try to forget the original story exists.
I'm going to start with TL-191 because most people are familiar with it. Forget everything you know about it for good and for ill. Narrow your vision and focus on the POD alone:
Robert E. Lee's Special Order 191, the so-called "Lost Orders", aren't lost by the Confederates and don't fall into Union hands.
That's it, that's the POD. Ignore all the consequences and ramifications deriving from that POD that Turtledove had. Let's just pose that POD and now ask, with all the analysis that AH.com can muster: what happens?