Today, Microsoft announced that it's releasing Windows 10 SDK Preview build 16278, along with Mobile Emulator build 15240. Of course, the Mobile Emulator build was released on August 22 alongside SDK Preview build 16267, so that aspect of the announcement was mistaken.
Sadly, the company's lack of attention to detail when it comes to Windows 10 Mobile is nothing new. The current development cycle of Mobile has been littered with releasing Fast ring builds on days where Insider chief Dona Sarkar said there would be no new builds, and releasing Slow ring builds without any announcement at all.
There's one known issue, which is the inability to compile apps on non-Windows 10 platforms. Of course, this only happens if you target build 16278, and you're probably going to be running the SDK on the latest Windows 10 builds anyway.
There's one listed breaking change:
ecmangen.exe removal from the SDK: Ecmangen.exe will no longer ship with the Windows SDK. Developers who rely on ecmangen for event manifest creation are advised to install the Windows Creators Edition of the SDK to obtain the file. Developers may also use notepad or other XML editor of choice for manifest creation. A schema file is available on MSDN to aid in manifest creation, for tools that support it.
Obviously, there's not a lot that's new. Microsoft announced in July that the SDK for the Fall Creators Update is now 'platform-complete', so from here on in, new builds will likely focus on fixes instead of features.
If you want to download the new Windows 10 SDK Preview build, you can find it here, along with Mobile Emulator Preview build 15240.