Hard to say. The clamoring for taxing unrealized gains seemed just as fringe to me, and now we've already got Janet Yellen trying to make it real.
Because the internal logic to pretty much anything falls apart at an egregious enough scale. 401(k)s are wonderful for nearly all Americans (although a weak replacement for pensions, and too many Americans start them too late for the miracle of compound interest to really kick in). But at the extreme end of the scale, the top half of one percenters pay little to no taxes as they take loans against the unrealized profits of their portfolios, wrapped up in complicated agreements and hedges. What works for 99.5% of Americans is broken at scale for the top .5%.
For better or worse, that's how a movement starts.