brehs now that I think about it, I get how "i" ties into the album. It's Kendrick getting into a car, turning on the radio and ironically hearing something positive, while his life circumstances are so negative. That's why the song starts out by saying "this is a world premier."
And the traffic sounds at the end would be Kendrick snapping out of the positive mood the song generated, and realizing he's still stuck in traffic/life/whatever.
The producer of the track said Kendrick asked him to make something super positive. Given that everyone keeps saying this album is darker, I'd bet that is the concept behind the single and how it fits. We know he had a recent session with Pharrell so I think that's where he'll get a single from, for next year.