The 9-9-9 Plan is a member of what I call the family of taxonomically equivalent tax systems, which define the tax base in an economically proper manner, albeit in different forms, and minimize the deadweight-loss tax burden on the economy.
In addition, Austan Goolsbee, the former chairman of Mr. Obama's Council of Economic Advisers, did pioneering work in the early 2000s documenting that the organizational form of firms is highly responsive to tax changes, arguing at the time that this significantly increases the likely deadweight loss associated with the corporate tax.
If instead these individuals paid the full premiums for their retiree health coverage directly, it would eliminate the deadweight losses caused by financing their Medicare with tax revenues. (Remember such deadweight losses harm all of us, not just those at the top of the income distribution).