Once a vanity domain is added for login purposes only, add an option to 'Disable' further DNS checks, and changes it's status to 'Verified'
If the added vanity domain is there for login purposes only, switch it's status to 'Verified'. The 'Setup in Progress' does not provide that any work has been made or is needed. In the 'Update DNS Settings' section, add an action box to check if the domain is being used 'For Portal login only'.
I just got off an O365 Support call about this. Please bring the "Domain Purpose" section back into the new admin center, or add a powershell way to set it. The current solution of turning off all DNS checks just because I want to limit a vanity domain to Exchange Online is not an effective solution. This was one of two features in the old/classic admin portal which was not brought across, the second being the ability to turn off dirsync (which has been added to powershell)
Michael Burke commented
Please bring the "Domain Purpose" selection to the new admin portal. Then when a domain is added that is only for user validation, allow the user to remove the services that are unused. This should allow the domain to go to validation mode without any edits (aside from the initial txt to check for domain ownership)