Why yes, yes it is. That indeed is the definition of the Fair Tax plan...
eliminate the tax on income - replace with a consumption tax on new (never before taxed) goods and services.
part of that is obviously repealing the 16th and making the taxation of income unconstitional.
It might be "the definition" of a plan but it isn't their plan and if their plan (HR25) was implemented that doesn't mean any other actions would be taken...
Their plan, HR25, doesn't legislate anything constitutional....but you knew that.