You wouldn't even need 100mph speedlimits if self-driving cars can avoid some of the common high-traffic pitfalls [eg traffic waves [1]]
It's likely that even at equal or higher density, self-driving cars will be able to have higher throughput with comparable speed limits.
Initially, though, it might be sufficient to "encourage" them by allowing them in commuter lanes. [this should even be trivial, because it should be pretty easy to find passengers uber-pool style if adding passengers would improve the trip]
Slight tangent but one of the most interesting parts (to me) of lane splitting on a motorcycle is getting to navigate through these waves and actually see the dense and sparse segments as you pass through them
It's likely that even at equal or higher density, self-driving cars will be able to have higher throughput with comparable speed limits.
Initially, though, it might be sufficient to "encourage" them by allowing them in commuter lanes. [this should even be trivial, because it should be pretty easy to find passengers uber-pool style if adding passengers would improve the trip]
[1]: https://en.wikipedia.org/wiki/Traffic_wave