https://forum.paradoxplaza.com/forum/developer-diary/behind-the-scenes-2-editor.1602378/
ROADMAP
The Editor is currently in beta and being tested by our modding beta group, which consists of seasoned modders and asset creators. The Editor will be released in several steps, the first of which will include map creation, asset import, code mods, and sharing those as well as savegames through Paradox Mods.
Creating custom maps in Cities: Skylines II includes what you might expect: Shaping the landscape, setting up water sources for rivers and lakes, painting in natural resources and forests, and setting up the basic outside connections for a city. But map creation also includes setting up the map’s climate, including its temperature variations and weather.
The initial release of the Editor supports the creation of custom buildings with more asset types to be supported in the future. It allows you to import custom .fbx files with a matching set of textures, set up color variations, decorate the asset, and tweak its stats to fit your new asset. You can of course also edit existing assets, giving your favorite building a new look through different color variations and decorations. All the technical information about modeling and texturing assets can be found on the official wiki, which will be updated as more information is available.
Last, but definitely not least, this update will support code modding. We have given a lot of the prominent modders from Cities: Skylines early access to Cities: Skylines II, giving them a chance to get familiar with the game and get inspired to create mods. That said, please remember that the game uses new technology and has a deeper simulation, so mods need to be created from scratch and nothing done earlier for Cities: Skylines can be used as such. We’re very excited to see what the modders create for this time around!
This first update will also enable sharing to Paradox Mods. Here you can share and download custom maps, buildings, and code mods, as well as share your savegame or download other people’s cities to explore. Paradox Mods will be available on all platforms, not just PC, within the limits of each platform. We’ll get into the details of what will be included for console closer to their release.
THE NEXT STEP
Following the release of the Editor our next goal is to expand its capabilities to include more asset types. We want to give you the ability to create your very own vehicles, trees and bushes, as well as the option to import custom citizen models. Both trees and citizens are more complex than their counterparts in Cities: Skylines.
As trees go through a lifecycle in Cities: Skylines II, from saplings to adult trees and eventually to dead trees, custom trees require several models corresponding to each stage of their life. Similarly, citizens go through different life stages which are reflected in their character models changing from children all the way to seniors. We’ll take you behind the scenes of character models in a future development diary which may help potential creators get a sense of what to expect once the Editor supports custom characters.