You will not get community support from Virtualbox if you have trouble with this process, as it’s against Apple ToS. The macOS Virtualbox option is designed for genuine Apple hardware. While it’s not exactly daily-driver level, the performance in Virtualbox wasn’t too bad! OS X has always been runnable in Virtualbox for a while, but the performance has normally been lacklustre. I had no expectations that this was going to work.
So what if you want to sandbox something? Virtualbox! That’s well and great, but I didn’t want to screw around with my partner’s Macbook. In the pursuit of Hackintosh, you need a Mac.