I would expect a regional system to connect an entire regional area.
Caltrain connects two parts of the Bay Area: San Francisco and the South Bay. BART connects the entire East Bay to San Francisco. In a functioning system, they would both just be legs and not two completely separate systems.
The only place they connect appears to be in Millbrae and not near any large hubs.
They will soon connect in San Jose.
I wouldn't consider "soon" to mean ten years.
Six miles, 12 billion dollars, opening in 2036.
https://en.wikipedia.org/wiki/Silicon_Valley_BART_extension
What's the holdup? Do they need to source more 5.25 inch floppy drives?
Don’t forget the SF Downtown Rail Extension, planned since the 1990s supposedly.
https://www.tjpa.org/portaldtx/about-portal
https://www.caltrain.com/media/17998/download
Is the argument just that the MNR and NYC subway, or Boston's T and commuter rail, are better integrated than BART and the Caltrain? Seems pretty great now but then I remember before the renovations at 4th and King.
My argument is that Caltrain mainly connects the two most largest and richest cities in the SF Bay Area, which are both population and job centers.
It would be like calling the Google private shuttles a model for public buses to follow.