1. To get from the East Bay to SF in the carpool lane you need 2 passengers (3 people total - or a car that only seats two)
2. The East Bay already has a pretty nice system for this called the Casual Carpool which is probably its biggest competition. The Casual Carpool is just a bunch of spots (usually BART Stations) where drivers can stop and pick up a few other passengers to get in the carpool lane across the bridge and usually the passengers chip in a few bucks for the toll. This system is pretty good and works well considering the need for 3 folks in the car to get carpool lane access. The Lyft model is a lot harder to coordinate picking up 3. The biggest issues with Casual Carpool are that there's no revenue for the driver and it's mostly one way (inbound in the morning). The eastbound after work system is not as efficient, there's a common pickup area downtown with stops indicating destinations but it can be hit or miss on whether passengers are there when you're ready to go home.
Long and short of it I think this is a Peninsula solution not really an East Bay to SF one yet.