I'd be quite keen to see this too, I run a Windows domain to manage the various users in my house. Everyone has a VM or two, some private shares and some "whole house" shares. Would be great to use AD groups for UnRAID share permissions.
My current workaround was to install Hyper-V (ugh) on my work laptop, spin up a third DC on it, join UnRAID to my domain, then decommission the DC.
Hyper-V is free in Win10 Pro and upwards, it's the world's worst hypervisor but as a workaround to get UnRAID on a domain it does the trick.
Alternatively, if you don’t have a spare computer you can install Hyper-V on, you could sign up for a free Azure or AWS trial and build a domain controller in the cloud. Once UnRAID is joined you just delete the account.