Aizen has prophesied his own destruction.
Way back at the end of the Soul Society arc Aizen announced that he would sit upon the throne of heaven which many interpreted to mean he intended to become a god.
Yet when Orihime arrives in Las Noches (chapter 240) Aizen describes her power as one that trespasses into the territory of god.
I'll let you connect the dots but bear with me a moment longer as well because there's a bit more.
Many people have criticised Orihime for being the damsel in distress so often and being generally useless in combat situation which is a problem in a Shounen fighting series. The most common rebuttal to that is that someone is more suited for healing and defence doesn't make them a bad person. This is true to an extent, though the appearance of the Combat Medic and Barrier Warrior tropes do erode it slightly but this isn't where the thrust of my argument is going.
My point is the fact that Bleach is a Shounen fighing series and while Kubo-sensei is not above messing with things (The substitute shinigami arc is effectively a gender reversed magical girl series for one) there is still a certain amount of formula at work here. Part of the formula that is still being played fairly straight is that emotional status and combat power tend to be linked. Ishida gets the chance to avenge his grandfather and goes One Winged Angel on Mayuri. Renji finally decides between duty and loyalty to a friend and his next fight he unleashes his bankai for the first time. Rukia finally realises that there are people who care about her and starts to come to terms with Kaien's death and next time we see her in a fight, she unleashes her shikai and one hit kills an Arrancar. Iba tells Ikkaku point blank that he can't achieve his full potential by hiding in hopes to remain in the 11th Division. Ichigo finally overcomes all his doubts and conflicting desires to unleash his true potential (in a rather disturbing fashion) and absolutely curb stomps Ulquiorra. (Notice Chad's absence from this list and his less than impressive record against higher ranked opponents?)
So the fact remains that Orihime has been dragged through the emotional wringer and it's her turmoils have been upfront and centre for an extended period. You don't do that to a character and have it so in focus without a reason. Combine that with above and you get the end result result that Orihime's eventual power up is going to be spectacular (a position I have maintained for quite some time). Perhaps even... godlike.
And it gets better still. I've said before about how Ichigo's fights have had an opponent that mirrored him in some way and it extends to other characters as well. Mayuri's torture of Ishida's grandfather gave them a connection. Kenpachi and Nnoitora are both battle-crazed Blood Knights, Mayuri and Szayel-Apollo was a Mad Science Duel. Stark and Shunsui are both powerful, intelligent and rather laid back. Soi Fon the lightning fast assassin fought the embodiment of slow creeping old age and I'm really hoping that gentle, motherly Unohana will be the one that fights the Espada embodying wrath. (I'm at a loss to explain Hitsugaya vs Halibel for I am to busy fanboying and laughing over Paku Romi vs Ogata Megumi)
So that leads us back to Orihime. Unlike Chad who has yet to meet his proper opposite number Orihime has had several opportunities that have now passed. There was Nnoitora who degraded her and then silenced her by sticking his fingers almost down her throat which despite the amount of service from some of the female characters is perhaps the most blatantly sexual image in Bleach and not in a good way. Next was Ulquiorra who had been manipulating her for longer and left her a mental and emotional wreck from which she has yet to fully recover. But he was steamrollered by Beast!Ichigo. Menolly and Loly who had tormented her got whipped by Yammy in a Big Damn Villain moment. However there remains the one who was the architect of her blackmail, capture and thus the subsequent torment. Aizen
Further more Aizen and Orihime make the perfect foils for each other. Aizen is cold, manipulative and uncaring. Orihime is sweet, almost innocent and above all caring. One betrays those who cared for them while the other forgives those who have hurt them most. One who seeks power and domination vs one who was granted almost infinite power that awoke to protect her friends
And so it stands. A conjectural edifice born out of speculation and a bit of Wild Mass Guessing but at least there's a foundation of evidence (or at least so I hope). Orihime vs Aizen! Let the final battle commence!
P.S. And before you ask, yes I do spend too much time at TV Tropes Wiki and yes, it has ruined my vocabulary.