I will admit, I'm tired of people bashing on her. And Kishi still hasn't developed her too much, however medical nin tend to be ignored anyway unless they reach legend status.. Sakura is a Tsunade knock off. The reason why she became a medical nin and why Kishi put her there is the following:
1) Sakura realised, that with her time with team 7, she wasn't able to actually fight, or at least keep up with the increasing strength of the others.
2) Sakura realised that she had amazing chakra control, and through hearing about them and reading/researching, she learned about medical jutsu and became drawn into it, upon said reading I'm sure she came across stories and medical journals of Tsunade and the Senju, this inspired her to even want to learn it.
3) Sakura's mind set has never been to fight or harm people, but aid them.. even in part 1. Not out of fear (well.. that's up for debate) but because she had no desire to fight, if she did she'd be like Ino or Tenten, but she isn't.
4) Kishi developed her in such a way in part 1 that it would make sense to pair her up with Tsunade to become a medical nin. I'm sure originally he set her up to be the brains of the group, but also to be the motivation in a sticky situation (like her being in distress...), but plans change and we all know that when reading Naruto.. with the plot holes. (They are there because Kishi changed his mind).
My thoughts? I think Kishi actually did the opposite from what you're saying here. He set her up to be eventually a side heroine, or one of the shadows. Not that it's a bad thing either, but I don't think we will see as huge of a character development as you claim is being foreshadowed. In interviews Kishi has even stated that he has kind of forgot about her. It's very clear in his writing that he's even moved on from team 7 in general for the time being and letting the other characters develop. The heroine role for now seems to have taken a focus on Hinata, not Sakura. I haven't even seen Sakura once since she stopped the Zetsu spy.. and if she has appeared, it was for such a short time I don't even remember. If Kishi wanted to develop her more, he wouldn't have totally left her out of the panels. He didn't leave the characters that we are seeing developed right now out from what I remember. So don't get your hopes up. Personally, I'd love to see her crawl out of her old hole and be up there with Naruto and Sasuke by the end of the Manga as the next gen of legends.. but. Yeah.