The one that comes to mind after Earth day...as a global population, we are consuming the planet at a rate that requires 1.6 Earths to sustain. IIRC, that goes up dramatically when you focus on the developed world. IF (and I know it's a big if) under/undeveloped areas grow to match the developed world, that number goes up to 7. We'll need 7 Earths to keep up. Not sure about you, but I don't have an extra earth hanging out under the bed.
Another one, probably a subset of the earth count, is deforestation and sustainable replacement. We're cutting down something like 4 years of forest growth every year. Yeah - great that we're replanting but nowhere near the replacement rate since clear cutting methods are diminishing the degree to which land can support forest growth as topsoil erosion take off when the forest is gone.
Anyway - rant off. I'm not sure why you're post struck such an energetic chord for me. Sustainability isn't usually my hot button but I too have been thinking about what the world looks like with no jobs. While I knew it was happening, the phrase used in the recent elections "You didn't lose your job to a Mexican, you lost it to a microchip" really captured it for me. The Terminator movies are great Sci-fi about what happens when robots and AI go bad. The movie that needs to be made is about what happens when robots and AI simply do exactly what they're designed to do. When all the jobs disappear, it's going to make Terminator look like a walk in the park.