I think a “just rebrand it and remove all mention of Oracle’s proprietary extension pack” fork wouldn’t require much “low level programming chops” at all. You could probably even automate a lot of it, with manual intervention only required for branding-related changes (which I assume would be rare). My biggest concern about doing it would be the macOS kexts - will Oracle’s trademark policy allow you to redistribute their kext binaries along with a fork, or force you to rebuild them under a new ID? If the later, will Apple approve it (for any special entitlements it might use)? Not an issue for Linux and Windows builds anyway.

Even stuff like RDP, I haven’t looked at the VirtualBox code in detail, but I assume there would be some interfaces to isolate display clients from the low-level technical details of the graphics card emulation-so it might not actually require as much “low-level chops” as you might think.

But your last point about not many people want to spend their weekends on it is spot-on: I myself am not volunteering to do any of this. Between my day job and a young family, don’t have as much time for personal projects as I used to, and what time I do have I’d rather expend towards other goals.