Because of the topology of the Bay we would basically have to build a levee all the way around it. IANACivil Engineer, but that seems like a big deal.
All I'm saying is that if you're looking to buy or build in the Bay Area do your homework.
A couple of years ago I was looking at buying a condo on the water in Redwood City and it dawned on me that, by the time I paid off the mortgage, it would be underwater both literally and figuratively. ( https://www.nolo.com/legal-encyclopedia/what-is-underwater-m... )
It doesn't make sense to build up new urban sites along CalTrain if we don't also deal with the effects of climate change, eh?