Huh? 600,000 people in the Bay Area's 7,000 square miles -- I don't see how the Seattle comparison of "83.94" square miles is related.
No residential neighborhood in the Bay Area needs to turn into "Manhattan" to house 600,000 extra people. If every block added a house we'd have extra housing to spare. Zoning prevents a ton of development, and everyone pretends they're fighting "Manhattan".
At Manhattan densities, the Bay Area would house 468 million people. That's not what's happening, and no one is advocating for that.
We don't need to build Seattle in the Bay to house everyone. We just need cities to stop dragging permits out years and every planning committee to stop saying "no" to any small increases in density.
How much construction it is isn't super relevant -- if it's profitable, it will happen!