It'd definitely be cool for city building. Like, I genuinely lose sleep thinking about how much I need this.
You wouldn't have the whole world accesible at the one time, but you could fly to a place in the world and 'choose' that region (like a big big square) and build your city there.
Something so many city builders lack, that only Simcity 4 really did to its max potential - region size. Not neccesarily map size, but the ability to really stack up towns and cities from different parts of a continent and have them all exist together, just as a visual thing.
To know that more exists than just the tile you're working on.With an Outerra based city builder, you could have your main city in some continent, fly up high in the air to see it from up there, then fly down to another valley many kilometres away to start building a satellite town. Then, the sheer joy of creating a winding highway to connect them, creating a train network to join up all your little towns and hamlets and satelite cities you've made.
So it's less about map size, (CitiesXL and Cities Skylines both had pretty big maps) and more about the *world* being there, being on earth, being on this continent, being in this region. Makes such a difference. No other game does it to it's biggest potential.
Outerra already has the ability to handle thousands of roads and buildings, so it's definitely capable of handling a city to an extent, and the road-building system is quite good.
Just watch this video Cameni posted and tell me it wouldn't be possible to take it a step further with much bigger selection of models, a few more road types, and connecting those buildings to a population
So it's definitely the most interesting long-term possible 'game' for me. I know so many people would appreciate and lust over. The idea that you could work on your region for many many years, slowly working your way over the continent to other places.
To deal with the challenge of rendering multiple cities, when you want to fly up to see them all, I thought of a solution. I'd say every half hour or so, the game takes low res aerial 'pictures' of each population center from 1k up, 5k up, 10k, 100k etc. And just stores them. So that when you fly up above the corresponding region and want to see all the city growth together, it can load in those aligned pictures underneath the atmosphere, without rendering a single little building.
This is SO possible. I know traffic logic and RDI is a pain in the ass to figure out in a realistic way, but that's barely the most important thing to me. I really just want to do what Outerra can already do, but with various road types, various house and building types, a few ways to draw parks (the way CitiesXL handles parks is great). Not to mention Outerra already offers zooming down to street level, walking around the beautiful natural world with bird sounds and wind. Imagine doing that but you're surrounded by neighborhood houses with laneways and parks, a suburban train line nearby.
The most immersive, grand-scale city builder of all time.