Yes there is a hard floor with the price, but there are two ways it could go lower even without driverless cars. The first is Uber's indirect vehicle costs (borne by the driver, but ultimately affecting the price floor) are very high. The drivers don't have any economies of scale in running and servicing their vehicles. A competetor that is optimised for running costs could undercut Uber.
The second way a competetor could undercuts Uber is by accepting a lower return on capital. Uber's cost of capital is very high compared to the cost of capital in the utility industry. It will be very hard for Uber to compete long term against a rival with low cost capital.
My expectation is Uber will win the battle against its venture backed rivals and will lose to a new competetor optimised for running and capital costs.
The second way a competetor could undercuts Uber is by accepting a lower return on capital. Uber's cost of capital is very high compared to the cost of capital in the utility industry. It will be very hard for Uber to compete long term against a rival with low cost capital.
My expectation is Uber will win the battle against its venture backed rivals and will lose to a new competetor optimised for running and capital costs.