If you compare Kirin's prep time to other jutsu's that take prep time (Sage Mode, Konan's sea of paper tags, or half of Shikimaru's arsenal), Kirin's prep time isn't that bad at all.
All you need to do is heat up the atmosphere to create thunder clouds. Shoot some fire dragons into the air, sprinkle some enton/amaterasu in there and you're good to go.
Sasuke was weak vs Itachi but now he could pretty much spam fire style/enton.
Also, jutsus like this scale up in power just as the user does. So if current Sasuke, (or post-powerup sasuke) used Kirin, it's safe to assume the bolt of natural lightning would be much bigger this time.
The reason people hype Kirin so much is because it's a badass jutsu that uses natural energy, which is 1 weakness of Juubi form. And that's why it will be used soon. Either against Madara or the Juubi itself.
If Kirin's prep time is so detrimental, as you all claim it to be, then how did Sasuke land it on Itachi? Seems to me that the prep time made little difference in that fight.