Your lack of faith in Kellhus is disturbing.
Good.
1. Kellhus saw himself within the inverse fire, not as fodder, but descending as hunger.
Assuming it was Kellhus doing the seeing and not Ajokli, blah blah blah, then yeah that's pretty strong evidence that his future in the Outside (should his soul get there) would not be one of the nameless tortured souls.
2. Nauir was described as a Prince of Hell by the judging eye because some souls were too powerful.
Described as Prince of Hell certainly. Not to prove or disprove anything, but I'm wondering generally if there was a 'because' clearly written in the book? The two halves of the above point are true independently, I'm just wondering if they were ever presented together like that.
3. All the gods exist outside of time in some fashion. So once you're a God, you've always been a God since even before the beginning of the series.
Pretty straightforward there - as straightforward as a-temporal beings existing in a linear time universe are straightforward, lol.
4. Nothing that has happened so far, contradicts TTT as outlined between Kellhus and his father Moe.
Any chance you can clarify this? What TTT was outline and not contradicted?
IIRC, TTT as presented by Moenghus was immediately co-opted by Kellhus, so in that sense Moeghus' TTT was destroyed utterly from the second Kellhus entered Kyudia. I'm guessing you meant that in a more general sense - so what generally is TTT you're referring too?
5. In the conversations between Khell and the unnamed outside entity, the outside entity says he wars with the God and to draw him out he needs to raze the fields. Khell says he is the one who tends the fields (paraphrasing here).
I always took this to contradict your main point here. It seemed to me that Kellhus' "but I tend the fields" was a defiant statement - basically saying "You cannot burn the fields as long as I am tending them".
But that Unnamed Entity is curious. It would be strange, from a plot/worldbuilding/thematic sense, to add in such a character with no background into book 6, not mention it again until book 8 and have it be some random God bent of usurping The God. Doesn't make sense. It almost certainly has to be someone (something) we've seen already.
Moe's version of TTT specifically outlined how premeditated disasters would keep piling on TGO. Kellhus sees farther but we're never actually told that he would reverse the disasters for TGO.
Same question above, is that really what Moe tells us about TTT? I don't remember that being the case. I thought all we really got was something like 'the holy was was necessary to unite humanity under one banner so that an army could be raised to contest the Consult before the No God awakens'.
Not that this diminishes your overall point though.
I suspect he's the outside entity Kellhus has been communing with and has been using his mortal past self as a tool.
...
I believe in his own Dunyain way, Kellhus, as an Outside entity, would do what he does and use anything and everything including himself. The endgoal is to take down the God.
I think that conclusion follows the assumptions laid out above, and if this is how things turn out I won't be disappointed.
I do think a slight correction though: taking down God is a stepping stone. Kellhus' goal is to become The Absolute self moving soul, and the only way to do that is to have no darkness preceding him, which means he must become The God (therefore killing it to replace)
I think of the meta clues of the series. If the last series is just the downfall of mankind, there's no narrative there. It's just losing and there's no point in extending the series. Since we know Bakker was going to end the series with AE, the closest way to end the series while having leeway to extend it by a few books is a bootstrap paradox. Originally the series ends with Kellhus completing a temporal loop, becoming the God he's always been the entire series. The extended series draws this process out.
I've been thinking about the story structure, or 'meta clues' a lot lately. There's a lot of theories out there that are at least internally consistent, but that don't really fit into what I'd describe as the theme (or worldbuilding, or plot development ... whatever).
I will correct one thing there though, the series was never to end with TAE - he only ever said he'd be satisfied being able to tell the story through TAE even if he never got to do the rest. There was always TNG (in its initial inception, TSA was a 3 book series, TNG as book 3).
For what its worth, I think you're right that if the story is planned to continue on as it has been, placing Kellhus in the Outside is probably the most viable way to continue on. That said, I suspect that the final few books in TNG series will be structured vastly differently to the previous books. More of an extended epilogue than anything else. Its for that reason that I don't believe we'll ever know who the Unnamed Entity is, or what Kellhus' final fate truly was. Again, that doesn't make your conclusion any less valid, I just don't see us getting an answer.
Cheers MGM

. Nice to read you again.