No quantitative predictive value. Fidelity's "answers" aren't exactly rocket science... they think that tax rates can go up farther than they'll go down.
But the interesting parts of the article are:
1.) Historical deficits, especially the Great Depression and WWII,
2.) Historical tax rates, especially the ones to contend with historical deficits,
3.) If your conventional IRA has been hammered down, then the taxable portion of the conversion is probably a lot smaller than it used to be.