Today, during a Windows Community Standup, Kevin Gallo announced that the next Windows Developer Day will be held on October 10 at 9:30am Pacific Time. Then, Microsoft "will discuss updates and new features for software development in the Fall Creators Update."
There's going to be something for everyone, including game, commercial, and consumer developers. For game developers, Gallo will talk about Game Mode improvements, the Xbox Live Creators Program, Mixer, and Windows Store improvements.
For commercial developers, Gallo will be talking about .NET Standard 2.0, Xamarin, Desktop Bridge improvements, and Windows Mixed Reality. Finally, consumer developers will have the opportunity to learn more about Fluent Design, Microsoft Graph, and Tooling improvements in Visual Studio.
Windows Developer Day isn't an event that you can attend in person; instead, it will be available via live-stream. Because of this, Microsoft is holding Live Stream Viewing parties where developers can get together and watch, in the following locations:
Of course, in between now and then is Microsoft's Ignite 2017 conference, so there will likely be topics discussed that we don't know about yet. You can sign up to learn more about Windows Developer Day here.