Welp this happened nothing like I'd imagined, but I guess I should have expected it to be bleak considering how the rest of the story has gone thus far. At least its looking like you're trying to follow canon so I can hope things will end up better.
Celestia really needs to get that happy ending considering what she's gone through and as oblivious as Luna seemed to Celestia's internal struggle I hope that she figures it out.
I really want Luna to find out what happened during her solo run during the crystal empire incident and her nightmares about Tartarus because that confrontation could be pretty juicy. She didn't seem to have her signature dream-walking abilities in the past and I'm hoping she more or less invents the spell to help her sister.

Damn. This is incredible work. As well, your musings on NMM and Luna are fantastic. I wish I had read something like this a few years ago, when I wrote about a NMM that was much more bland. Definitely gonna follow this story closely.

A sudden rush through to read all this. It's heartrending, to just see Celestia become as much a porcelain statue as those baubles - to her, anyhow - she keeps scattered about. She is mad, indeed, but it's a controlled madness, and when one locks oneself away in such a shell...you don't realize what you miss, until something forces you to examine it, truly examine it.

And then it's years of struggling to pull free - for a mortal. For an immortal? Who knows. But all this time, you feel regret for what you lost, what you let pass you by because it was safer inside the armor. And the hardest part is you become unsure. Are you still wearing it? You want it off, yet then something happens. You know you should feel more horror, more sadness, yet all there is is a numbness, a sense of 'I should be doing things here, but..what, exactly?'

So...the modern her rings terribly familiar to me, because those aches I know too well and wish I did not. And this story deserves to be much more widespread than it is.

Luna, please...
Break. Her.
As calm, comforting and wise as she may seem, Tia has gone mad beyond even what you inadvertently did to yourself.
And her mask must be broken if there is to be any healing.

You have NOTHING to apologize for in regards to your theory. You bring some excellent points. Stories where Celestia is all are a veritable bit a dozen. Good stories, to be sure, but it is rarer where Celestia's flaws and foibles are made so prominent without being deliberate if you catch my meaning.

In the end though, short of Daybreaker type tyranny, your take on Celestia and the stories I'm thinking of have a direction in common. Celestia would strip herself and maybe Equestria as a whole given enough time (cough immortal cough) of all the things that make life worth living. She seeks perfection and a sterile unchanging monochrome existence free of doubt, fear, or pain. But this corpse that wears her face would go beyond that. It would paint the world solid grey.