People presumably think it is. As a visitor there now a lot of SF looks quite low density low rise, but a lot of the buildings are very pretty and the low rise wooden houses are part of the charm. Not sure how much less dense than Tokyo it is but maybe 4x? As a Brit I love the history, but there are probably parts that could be rebuilt. But there is a high risk that they won't be built as high density, the fact that the proposal includes affordable is because the builders will infill high end mostly. You need to allow rebuild of low density at eg 10x at scale to get a fall in prices. Builders don't want that.