I'm here on my once-every-6-months journey for news and water.
I'm not convinced that there will be a SC5, but if there is, I'd like to see the following changes:
1) Multi-level water and surface water.
2) A water table, where we can sink water wells.
3) A less-tedious way of managing water. I hate laying pipes, even if they're only every 11 tiles or so. That's still too tedious. I'd rather clean my toilet. Make the job less tedious by giving us an auto-pipe button or tool.
3) Natural resources at different places in our regions. Like oil, coal, diamonds, iron ore, plutonium, fresh water.
4) Let us manage those resources. In God mode/Region we can select unlimited or constrained. For example, under constrained, we would need to have our cities adopt mass-transit and alternative fuel sources, or we could run out of oil.
If I get those items above, I'd be happy, and I promise I'll shut up about Earth-orbiting cities and underground/undersea cities.....