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 apply AI/geotagging to develop a piece of permaculture/landscape restoration software, with the ultimate aim being that the user inputs where they are and what resources they have (human labour time, tool access, seeds/starts, etc.), and the AI outputs instructions like 'build this berm and plant these trees in this place because it will have xyz knockon effects that will save time/increase odds of success of these other actions'. the other end of this would be allowing users to share information (I have these resources to share, I observed this or that species, this technique did or didn't work) or connect to help other projects ('I have an afternoon to spare, what can I do to help in the community?'). finally, integration of broader scale community needs for planning purposes ('this region is going to need x saplings by spring next year, who is growing them and how')
I want this so much.