San Pablo is State Route CA-123 through Berkeley to North Oakland to Emeryville, though it appears that south of 580, google maps doesn't show it having that designation (i.e. it might have been "relinquished" by the state to the city in that portion some time ago). However, because that 34th St. at San Pablo intersection is just one block from the 35th/36th St couplet which probably is regarded by Caltrans as a freeway on-ramp connection from CA-123 to 580, it means that Caltrans likely has significant purview. So, not saying that it is impossible, but a roundabout might be rather unlikely to be viewed with favor by Caltrans there. Also, roundabouts are not always blessings to peds, b/c they are generally used to replace a signalized intersection and maintain car through-put. The Piedmont/Channing one has a very different context - far away from a freeway and not just off the end of a designated state hwy.