I do not know what Seattle is going to do, but usually they only close the street for motorized through traffic. If, say, you were to place bollards in the mid

I do not know what Seattle is going to do, but usually they only close the street for motorized through traffic. If, say, you were to place bollards in the middle of a block, every home will still be reachable by car. But as only residential traffic uses the road, the volume is greatly reduced, making it possible to dedicate space for pedestrians and cyclists. Additionally, the bollards will still allow these to pass, so it can be a through road for cyclists. So, if anything, it is a net positive for the residents.