It's unrealistic because it's not even being talked about yet. HSR is already being built, and will complete in the next 10 to 20 years.
By the time people start talking about BART SF-SJ, doing the hundreds of expensive studies, find funding, convince NIMBY's up and down 101, we are talking about 30 years of talking and not building. What will the world look like in 2046? Maybe we will all move to Shanghai by then.
The NIMBY's up and down the peninsula are the most stubborn NIMBY's. And they have lots and lots of money. And they don't care. They are still fighting Caltrain, something that existed before they bought their precious houses. You want to convince them something new should be built in their turf? For the public good? Not gonna happen.