Sakura getting Sage Mode.
First off, I wouldn't mind it, I wouldn't mind it if there was the tiniest bit of foreshadowing. As of now, you'd have to be seriously delusional to think there's enough background for Sakura to get Sage Mode. It would be a major Asspull. Yes, there is, right now, some foreshadowing about Sage Mode being the way to defeat Obito. But it isn't foreshadowing on Sakura getting Sage Mode, please draw the line.
Second, it feels really wrong when a character gets two consecutive powerups in the same fight. It's a staple of Deus Ex Machina (or being a bad guy in DBZ). Sakura already pulled her Byakowhatever (not bashing, I just can't remember the name) a few chapters ago, had her time to shine, and it would be bad writing to have her pull something else out of her buttocks now. Why? Simply because it would break the pace. Each time a new character gets in the fight, we lose one to three chapters worth of development in the fight. We'll already have to see Madara's Trump Card, and the 5 Kage + Oro and his team come to battle, Minato giving Naruto the other half of Kyuubi, that's quite enough subplots FOR A SINGLE FIGHT as it is.
Lastly, even if I do believe she NEEDS something else to be relevant and finally worthy of her "main heroine" role, there's absolutely no way a Sage Mode would put her on par with Naruto and Sasuke. Sure, some Sage Mode look reaaaaally stronger than others (Naruto's SM looks like a joke compared to Kabuto's) but the fact still is that her covering such a huge gap of power with just a Slug Sage Mode would feel like... Well, you know.
PS : I don't remember who, but someone here said :
"Sakura is said to be stronger than Tsunade who was stronger than the Raikage, so she's at least Kage level"
I'm sorry, what!? She lacks speed, and most definitely TONS of other assets to make her even half a decent Kage. I'm not going to call anyone who said this a Fanboy/Fangirl, as I can see where you come from with such logic, only it's really not how it works.