I don't think that an item switch menu would work for Mario Kart. Unlike Smash Brothers, the items are balanced against each other. If you take some out or use only a certain one, then things just won't work. Maybe there are more item options they could add along the lines of the "balanced, strategic, powerful" choice available in Mario Kart Wii.
As for myself, I agree that despite how similar they may seem, every Mario Kart game is different. I'm no fan of the series, and the only one of them I like is Mario Kart Wii. So for me to get a new game in the series, it'd take a lot to entice me. When I saw the transforming karts in the E3 trailer, I thought it was really cool. However, everything I've seen since then, from going back to only 8 racers to the lack of characters, vehicles, and modes, makes me feel more and more disappointed. And now, hearing that the transformations don't add as much as they should solidifies my decision that the game isn't worth full price. I'll be picking it up once I find it on sale for half that.