In fact, Oracle lists no Mac guest support there (for OS X 10.11 and later). However, I wonder if that is based on non-Mac hardware? My question was about running VirtualBox and new macOS versions on Mac hardware - though with 64-bit Linux as the host OS.
VMware promises to at least run Mojave in a macOS VM:
VMware said:VMware Fusion Features
Ready for macOS Mojave
Launch virtual machines on Mac with macOS 10.14 Mojave, including APFS support, or safely test the latest macOS in a sandbox on your current Mac without disruption. With an updated UI and customizable support for the latest Touch Bar enabled Macs, Fusion is better than ever.