I know people were talking about it, but a skill tree is a great idea imo. Instead of being a jack of all trades, I think having to put thought into a specific route would be a wonderful idea.
You're right, the levelling system is due a revamp (it's not that different from how it was in the original version of the game, but a lot has changed since). I'd love to add skill trees and make levelling feel more like a journey. Imagine Feeder, Feedee and Fitness skill trees, with, say, 50 levels, and lots of decisions as to which upgrades to pick.