That's certainly an issue, but even without that problem this would be an enormously expensive project. There's no room for this on the bridge now, so it would be a whole new structure on one side of it. I love riding the path to the island from Oakland, but I have doubts that a path from the island to SF will ever happen. Maybe a little more likely is ferry service from the SW corner of Treasure Island to SF and/or a cycling shuttle bus. It's a pretty long distance to cover, and usually with a headwind going west, so there probably wouldn't be too my bike commuters.