But You know... becoming princess has rather nothing to do with replacing Sunset.

You know even if Sunset hadn't escaped(it was told, that this was escape, not banishment) Twilight still would be Celestia's pupil(maybe not favourite, but this doesn't impact on becoming princess). And i really don't think that Twilight become alicorn beacause of being Celestia's pupil... it happened because she was destined to becoming an alicorn(Celestia herself say this - even if not literal). I think Sunset is destined to become alicorn too... what more i think it happened in Friendship Games. I say about her transformation at the begining of fight with Twilight.

And about this "destined"... in reality i don't think Twilight/Sunset become alicorn... i think they both ALWAYS WAS!

"Why?/How?", You can ask. Well it's simplier than it seemed to be. Even before watching episode "Magical Mystery Cure" and hearing "Celestia's Ballad" I theorise(i don't rememeber if i knew already that Twilight will become alicorn... but i think i knew...), that all alicorns weren't born in alicorn forms - they were born as unicorns, pegasus or earth pony(maybe without two last option, but rather with - this what i know about Cadance case confirms it), so at the beginning they all are "hidden" in form of "regular" pony, usualy not knowing their own true nature and true form. But during some important events in their live they transform into her/his(I know, we've seen only female alicorns... but who say there wasn't/can't be also a male alicorns?) true form. This is what happened to Twilight in season 3 final, and this is what i think that happened to Sunset in Friendship Games final(and the video "My past is not Today" has announced this - You know there is some similarity between and of this video and this how Twilight transformation look like).

This what Celestia said during her ballad confirm this theory i think. As well as beginning of season 6, where is clearly told that Celestia, Luna and Cadance WEREN'T born as alicorns - what my theory already predict(about Cadance it was mentioned in some book, that she was some time ago a pegasus... which i didn't know creating this theory, but this half-canonic source is still just next evidence for it).



And about earth-Sunset... right... question about her I ask myself many times... I even create some theories about what person she would be... But i really hope she someday will be shown in the show.



And... can You say more about this alternative timeline? I really like Sunset so it seems quite interesting for me...

(And if You can't understand something... sory, this is propably because of my weak english)