Between the holiday season and the fact that Microsoft is transitioning to the next Windows 10 development cycle following the 20H1 update, it's been some time since we last got a new preview build of the Windows 10 SDK. Today is the day, though, and Microsoft has released build 19546 of the SDK for users in the Insider program, making it the first in the new development cycle.
Because Fast ring builds no longer refer to specific versions of Windows 10, it's unclear whether we can say that this build is preparing for the next feature update. And since there's no blog post for this release yet, we don't really know what's new in this build, either, or the exact requirements to use the latest build of the SDK.
However, it's safe to assume that the requirements are fairly similar to what we've seen so far, meaning you'll need to be running Windows 10 Insider Preview builds, and it should require Visual Studio 2017 or newer. You can also run the build alongside production builds of the SDK, but apps you publish on the Microsoft Store need to target versions of Windows that are already generally available. Of course, that shouldn't matter too much since there hasn't been much in the way of new features in Windows 10 vNext builds so far.