The update will include new color tools, like color wheels and a white balance picker, with new controls for the color board. It will include support for HEVC, the new video format introduced in iOS 11 and macOS High Sierra, and direct import of iMovie for iOS timelines. The new version of the software will support VR and HDR workflows.
No specific release date for Final Cut Pro X 10.4 was announced, but Apple did say that it's coming before the end of 2017. Final Cut Pro X can be downloaded from the Mac App Store for $299.99. [Direct Link]