Even though Windows 10 SDK Preview was only released six days ago, Microsoft today announced SDK Preview build 17115. There's not much that's new, considering that its predecessor was released after Windows Developer Day, and was considered to be feature-complete.
There is one known issue though, which is that you won't be able to install this on a Windows 10 build that's not a Redstone 4 Insider Preview. This is a strange known issue, because it comes and goes. In SDK Preview build 17110, it worked on the current version of the OS, and a few builds before that, it didn't. It's entirely likely that the next SDK Preview will work on all versions of Windows 10 as well.
As usual, you can use this SDK in parallel with other Windows 10 SDKs. That means that it can be used in a production environment, although your apps should still target an earlier version of Windows. Apps that target version 1803 are not yet being accepted into the Microsoft Store. The SDK is only officially supported by Visual Studio 2017.
To download the latest Windows 10 SDK Insider Preview, you can find it here.