@Rainbow Dash is best pony  
Basically this.

I love this idea! But what would Equestria be like if this happened instead?

@Background Pony #845B  
Wall of text + broken English = tl;dr. Good try, keep working on it.

1000 years a go celestria/luna will do same for equistria! and will be more hard for luna but she will do it! she will everything celestia a do for equestria for 1000 years! do better then celestia? no! luna fear more to make mistake then celestia! luna will make more mistake then celestia a do but like the princessshe is, she will do her duty! luna control the sun will be hard for her but she will do it! she care for equestria like her sister do! and for those who think daybreaker banishing can still control the sun? no! why? the element of harmony seal all magic power! so daybreaker will never control the sun were she banishing! is the same for nightmare moon! luna is not as powerfull as her big sister who is better of all thing she do! but yes on this time line is luna will more love then celestia! i think of celestia who better on everything but no pony care! she save the day form all king of evil but the eyes of pony is on luna! an yes the pony look more the night then the day! she will become daybreaker! were see her mistake she will to clame her sister but she will fail like celestia a fail to clame luna and will end the same way celestia a do! SEAL HER OWN SISTER TO SAVE THE WORLD! luna will feel so hopeless to not save her sister! for luna will were hard to not be powerfull as her sister for save celestia! for celestia her a feel hopeless for not be more powerfull as nof for save luna! luna will cry a lot like celestia a do for not save luna! and no eternal night! all food for pony need the sun! no sun mean death! the eternal is eternal cold! so the pony will by not fead or by cold! all the plan will die fast with no sun! luna will control sun intand to fond way to survive to a eternal night! so your eternal night fan can shut up! in the real equestria time line , luna learn equestria will die by the eternal night! she know the pony will not survive of this! and she will never do it again! she learn by the time of be nightmare moon were she be save by twilight and her freinds! you think she will do again? think again! luna is not da stupid! she learn with her big sister and she dont want hurt celestia again! celestia be in sadness pain for 1000 years and is take all this 1000 years to heal and the return and save of luna heal celestia! and what a help healing her broking heart is all stundein and fond cadance a help her broking heart to heal! and were luna be turn back to her self and be re-united with luna a finish to heal her! yes she cry of be re-unite with luna and is the same luna , she a cry for be forgive for what she a done! who dont want a big sister who so forgivefull? not me! i want a big sister like this! so if is luna be seal celestia, luna will be sorry for not help in the past! well is will the same thing! luna will do all for the pony love the day as the same the night! like celestia a do for make the pony to see the beauty of the night!

@Background Pony #3F1B  
This is a great idea. Are you a writer? If not, can you commission this from someone on Fimfiction?

Luna cannot carry the weight of the sun and the moon on her own at this stage, and Daybreaker with her limited power makes the sun actively resist Luna’s attempts to raise it. The land is cast into eternal night.
 
Yknow this could be a neat AU. Luna finally gets what she wants, being in the limelight with only her night. Though this would never be how she’d imagined it.

@Neko Majin C  
But into the stillness, I’ll bring you a song.  
And I will your company keep,  
Till your tired eyes, and my lullabies,  
Have carried you softly to sleep.

@ZONESS  
The scenario I can think of is that the stress of running a country and being the one in the limelight eventually causes Celestia to crack and become Daybreaker, making Luna have to use the Elements of Harmony on her sister to keep the world alive.

@Neko Majin C  
I knew something was missing!

Not bad.
 
Though I’m sorry to say that the situation doesn’t really work in reverse. Luna felt neglected because everyone slept through her nights and only seemed to appreciate her sister’s days. How do you successfully reverse that? Is this version of Equestria populated by bat ponies who are all nocturnal?
 
I’m giving this too much thought, it just got my mind going is all.

I like this Alternate Universe but still pretty sad… :/ and last panel… hurts my heart

Fate has been cruel and order unkind.  
How can I have sent you away?  
The blame was my own, the punishment, yours.  
The harmony’s silent today.