Visual Studio 2017 was released after the most recent version of the ArcGIS Runtime SDK for .NET, so it is not yet officially supported, and the VSIX installer does not yet recognize it. Please see this help topic for information about the supported IDEs for the various SDK platforms.
While the VSIX installer does not recognize Visual Studio 2017, you can still use the SDK within 2017 by referencing the NuGet packages directly. Although not officially supported, we've met with success when trying this internally. For guidance regarding how to reference the SDK via NuGet, see the section Referencing online ArcGIS Runtime SDK NuGet packages in this document.
We of course intend to support Visual Studio 2017 in our forthcoming release.