Is TFSA income eligible for Treaty benefits?

Art. XVIII, para. 7 of the Canada-U.S. Treaty indicates that a qualifying U.S. beneficiary of a Canadian exempt trust may elect to defer U.S. taxation on the trust income until distributed, if the trust was "operated exclusively to provide pension...benefits."  Notwithstanding the "conservative" position of the big four accounting firms to the contrary, Nightingale and Turchen argue that a TFSA qualifies for this treatment.  ("'Exclusively' is a bit of a loose term.")

Neal Armstrong.   Summary of Kevyn Nightingale and David Turchen, "The US Tax Implications of a Tax-Free Savings Account", CCH Tax Topics, No. 2146, April 25, 2013, p.1 under Treaties - Art. 18.