either you create a cultural norm where tipping isn't allowed or expected, which Uber has effectively done, or you have a situation like restaurants, where the tip may as well be part of the price, unless you're cool being the asshole who doesn't tip, which most people aren't.
if tipping is an option, through a kind of cultural game-theoretic pressure, the situation will always devolve into the restaurant norm. at least that's how it is in the states, and short of massive cultural changes i don't see that changing.