I see the idea of the theory, but the one thing that's not really giving me any belief is because on an event in S2 E20. Cerberus' arrival and the mention of Tartarus, if there's any influence in the show it is most likely from Greek mythology.



Plus as all information in the show is considered canon against all others and nothing has stated Celestia is a deity so I don't assume she is one. (Since one doesn't need immortality to live 1000 years, eternal youth works to, or the fact she and Luna were the only ponies who when using the elements used All 6 of them at the same time (Celestia proved that it was possible during the original NMM incident so I'd assume Luna did as well) and the elements' first known use was their's so one could assume they're given eternal youth by the elements so they could keep harmony. (the elements aren't exactly self-mobile))



Though if Discord is needed for anything its possibly the rumored Bigger Bad that's assumed to exist. (TV Tropes states its possible there was someone responsible for making NMM, possible freeing Discord, helping Chrysalis find Equestria, and even having Sombra attack the empire. Wouldn't be surprised if its a fallen Alicorn or something that's even mightier than an Alicorn. (In fact my one friend stated after the finale he wouldn't be surprised if its actually Starswirl the Bearded.))