This map outlines a plan we've looked back at before—the 1911 plan, which was brought back to life in the 1930s, had the Hudson River getting drained and paved over. This would have connected Manhattan to New Jersey, creating 10-square-miles of land, and relieved traffic congestion with subterranean tubes and tunnels.
This map shows that the plan would have also absorbed Governors Island, and the NYPL believes Ellis and Liberty Islands, too. They point out today that "in a boastful or optimistic flourish, the red sections by Battery Park represent lots that had already been sold. The black stripe running down the center is a three-tiered transportation artery: train tracks on the bottom, lanes for cars in the middle, and an airplane landing strip on the top."
A few more crazy plans that never happened can be found here. And you can check out many many many more maps at the NYPL's Digital Collections page—recently they digitally released 20,000 maps from their collection!