Business and practical considerations will mean that BMW's and other automakers gradual approach to automation will prevail. A gradual approach allows automakers to recoup their investment immediately, and allows automakers to fine tune their technology as each aspect of automation is rolled out. It is also important to note that regulatory agencies will react and set the rules for new autonomous vehicles on the road based on the technology that is on the road, so those carmakers rolling out the technology first - those with a gradual approach - will have a greater input on the regulatory nature of that technology. The risk for Google as that as the other automakers will end up defining that regulatory environment, their technology will be obsolete from a regulatory standpoint by the time it is rolled out.
As much as I like Google's approach from an engineering standpoint, the truth is Google is already being left behind in autonomous car technology. Other auto makers are already introducing various aspects of self driving - from automatic emergency braking, lane assist, adaptive cruise control - so that by the time Google has their self-driving vehicles ready for the market, the major automakers will already have a road-test, established and entrenched set of technology they're working with.