My megaproject ideas are mostly pretty standard. I'd build a high speed rail network across North America, and build and expand metro and regional rail systems in and around every city. I'd turn all cities and suburbs into fifteen-minute cities. I'd decommodify housing, and build ten million units of public/social/non-market housing, mostly three bedroom units. I'd link those last three policies together by building TODs around the new Metro and rail stops. And I'd build bicycle networks in every town and city and connect them to the TODs. I'd build bridges and walkways across skyscrapers. I'd put a bidet in every American toilet (uses less water than toilet paper apart from being more comfortable). Fiber internet in every home. A heat pump in every home. An induction stove in every kitchen. Phase out fossil fuels and power everything with Pumped Storage Hydropower and Geothermal. I'd make the US go Metric.
But my truly crazy, obsessive idea would be to bring back the French Revolutionary calendar. Or I'd purge all French influences from English.
I'd take the best aspects of metric and amerikkkan measurement systems and invent DOZENAL METRIC. In fact, all math and counting will be done in base 12.
Build a railway through central America, terminating in Brazil, up through Canada to Alaska and then across to Russia.
Switch the internet from a server-client infrastructure to a p2p one with a small cache on every router using something like IPFS.
I appreciate what you're trying to do, but between the earthquakes and the 70 foot tall waves on a good day building a bridge across the Berring sea is going to be one of those "10,000 workers are interred in the foundations" projects.
China is already considering using robots to build dams. Since we're talking pie-in-the-sky already, let's just have robots build it.