Ratings already replace tips as an incentive for good service, in a far more transparent and actionable way.
And if drivers start getting tips regularly, you can guarantee their overall earnings won't go up -- Uber will simply pay them even less, because they can. Whether payment is technically part of a base fare or tip doesn't do a thing to change the law of supply and demand.
(Example -- how restaurants pay waiters far less than minimum wage, and are legally allowed to, because the tips make up for it.)
Moving back to tips is a huge step backwards -- especially when forward-thinking restaurants in NYC are moving away from them as well.