Colossal Order has been giving updates on the development of Cities: Skylines II's post-launch updates for weeks now. The latest developer blog from Colossal Order CEO Mariina Hallikainen covers the upcoming Editor for modders, the next major update's release timeline, and other aspects.
The studio already revealed a couple of weeks ago that official tools for editing the game's assets and maps is still in heavy development, and that a preliminary launch can't be expected until at least January. However, today an early access phase for the tools were announced.
"We would like to invite all mod, map, and asset creators to join early access to the Editor for a few weeks before its release so you can see what it is like," says the studio. "Test out your already created mods, and share your feedback with us."
Sign ups for the "Editor Early Access" can be found here. Keep in mind that only a select number of slots will be available. Creators can brush up on their modding skills using Colossal Order's newly updated asset creation-related wiki page here.
There is some bad news though. While an early version of the Editor has been unlocked by modders from within the Cities: Skylines II's current version for some time now, saves affected by it may not be compatible in the future:
"This is not to discourage you from working on your mods but rather to try and openly share what to expect. Some of the most notable changes will be in how the maps are saved so we can’t guarantee the maps saved on an unfinished version of the Editor will work with the game in the long run."
As for the promised bug fixes (mail and export), performance improvements, and other high priority changes, the studio says that a "bigger patch" should be arriving in December with all that and more. Following it, the development team will be taking a three week break over the holidays.