It looks like an overpriced dream. If I'm understanding the proposal correctly, there will still be the container port blocking the waterfront south of Jackson Street, so that section should stay elevated to reduce the length of the tunnel.
I don't really see the current viaduct as much of a barrier; I'd rather walk under it than cross a high volume, 6+ lane surface street at grade.
In my opinion, people who dislike freeways need to live in a medium sized city without any, and see what fun it can be to get across town, especially when the arterial system also stinks.