“So, it is done. Is that what you wanted?”
“I didn’t plan all of this, especially the filly. But it turned out even better than I had hoped. All the pieces are finally falling into place.”
“Your plans are too convoluted. No wonder it has taken you so long.”
“You know I had to wait. I couldn’t afford unnecessary risk.”
“What about the risk of keeping me in the dark?”
“All the better for you to play your part. Don’t you trust me?”
“Should I? After what you’ve done?”
“You know that’s the only way. The pawns are on the board, and the game is on, but we’re aiming for a very specific outcome here.”
“Can’t we find a different way to communicate? This enforced vagueness is getting on my nerves.”
“It can’t be helped. It’s hard enough to hide from the Amaranthine. Dissonance echoes. The last thing we need now is -”
“...a prophecy.”
"And as for the plan, Do not worry. I’ve had thousands of years to become good at this. When they finally see it coming, it will be too late.”
Something else occurred to me.
Luna's declaration of war is dramatic, sure, but how's she gonna convince anyone? Are they just supposed to take her word for it that the M6 killed Celestia and are now enemies of the state?
9783781
Just last week a magical intruder accompanied by Applejack broke into the castle, incapacitated several guards, and after briefly fighting both princesses, disappeared with the Elements of Harmony (both the items and the ponies). There was also an explosion in the castle dungeon.
It might not be common knowledge outside the castle, but everypony in the aristocracy, and the military knows.
Last night, creatures made of living nightmare appeared in the sky near Canterlot - Luna fought one while Enigma helped the air force defeat another. There was an alarm heard in the castle dungeons again.
And while it's definitely a closed casket funeral, Luna has a very solid proof that Celestia is dead.
Also, consider pony herd instinct. On several occasions in the series, when everypony panicked, Twilight was able to take command simply by behaving like she knew what she was doing. Ponies look for a leader when they feel lost - and right now, a status quo of a thousand years collapsed overnight. I'm pretty sure, as long as there was a way to raise the Sun, whoever walked through that door with a retinue of palace guard could give a similar speech and be just as convincing.