Another person researching heavily the juggle propperties of SFIV… Sadly it wasn’t as simple as i originally thought.
Though i’ve researched generally the same things you have, i gave them different names so you’re terminology is messing with me a bit (For example LK Tatsu i gave a JP (Juggle PRoperty or Point) as 0, meaning the character is in a juggle-able state, but can be hit with anything of any value)
Akumas EX Tatsu, if we go by Ryu would have a juggle propperty of 5, it is however very difficult (even with Ryu) to get all 5 hits to hit.
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The problem with Akumas is it has some peculiar propperties such as a kind of Suction. Which may effect it’s aerial propperties. (It could simply have different points)
Though you’ve explained this to a tee, almost exactly how i’ve ended my refinement of the mechanic (With a bit of help)
Sadly… because alot of attacks have varied characteristics on Counter hit (Sagat T-Upper, Chun Li LK Normal little flip kick. FA LVL 1 & of course Ken SRK) or hitting characters while in the air. It makes it exceptionally difficult to thoroughly test moves. IT is certain some moves have counter reset propperties (Dahlsim Super for example)
If i really want to simplify it for a quick explenation it simply say
“for every extra juggle you do take away one hit of the following move”
In terms of Akuma i’ll add “Shaku however, will hit one extra time”
That’s really the simplest can do it, disregarding all moves with special propperties.I say this because, for the most part it is generally correct.
To make things harder to test though. Try this
Abel -> Cr.HP
1st hit on a grounded opponent = conventional stun. On aerial opponent = Reset(No juggle potential)
2n’d hit on ground opponent = Juggle potential 0 (in my terminology it means any hit will hit, the best state for juggle) hitting on an aerial opponent = Same.
Now, if you hit a character with the 2n’d hit -> Roll then hit a character with the second hit again. What state are they in?
… Juggle potential 1.
Now it does surprise me that the Capcom team forsaw this mild exploit & resolved it before it could be abused. My point is going by conventional rationalization of how we’re percieving the juggle mechanics. They still have the ability to manipulate there own system for the sake of balance or exploit purposes. We know they’d allow the EX SRK -> FADC -> EX SRK -> FADC -> EX SRK -> FADC, because they know that on a rea game, it’d never be done & can’t be exploited. At most you’d get 2 HP SRK’s where the second hit is the only hit that hits on the second SRK (Causing Juggle Potential 0 again)
But with Abels Cr.HP you can basically do the move again & again in the corner. (You can roll, but this is the easier alternative)
Here’s something i don’t understand… Do this combo with Abel. (Has to be mid screen)
Cr. HP (Hits high, only secondhit hits)
HK Roll
Ultra (Doing it backwards, the roll crosses up)
= Ultra hits
Now do this
Cr.HP (Last hit)
LK Roll or FADC
Cr.HP (Last hit)
FADC BACK
Ultra
= Ultra hits = Ultra has minimum potential of 1
But do this
Cr.HP (Last hit)
LK Roll or FADC
Cr.HP (Last hit)
HK Roll (Cross up like the first combo)
Ultra
= I have never been able to achieve a hitting Ultra with this
On a side note, Abels Sky Fall (Air throw) has a 0 JP (Must hit a freefalling opp) EX has a JP of 1. Do EX SKy Fall at the end of the final combo, it looks great 
Hope that made sense 
I figured most of mine out originally by simply fucking about in Training, at first i simply thought it intertwined with the amount of hits in a moves (& that normlas were void of any juggle potential) but then i did a Counter hit SRK with Ken & shit got interesting.
As far i’m aware KEns 2 infinite juggle hits is one hit of his EX SRK (Last hit) & the first hit of his Aerial EX Tatsu.
Ialso have a relatively large list of Moves with 0 Juggle potential, in my terminology that basically means the same juggle propperty as Akumas LK Tatsu. Should the OP or anyone here want them, i wouldn’t say it’s a complete list though, that’s awork in progress.