Hahahaha.

https://en.wikipedia.org/wiki/Dumbarton_Rail_Corridor

Check out the storied history of RM2. Taxpayers literally voted to raise sales taxes to fund a rail corridor, and the money was reallocated to a different county for an unrelated project that did not benefit the counties in question. Never mind that an actual functional Dumbarton Rail could be a huge improvement to life on the Peninsula if done well.

Imagine a genuinely fast transfer between any one of the Caltrain stations (say Palo Alto or Menlo Park) and one of the East Bay BART stations. Of course, getting the western portion past all the expensive neighborhoods in the way sounds like a real mess.