This article is false. (Regardless of whether Quora will or will not grow.)

Many of the arguments should have been tested against Facebook: elitism didn't slow the spread of Facebook. In fact, it was likely a main driver of growth in the world's most popular website. It's not surprising Quora has been modeled after Facebook since Quora is made up of early Facebook alumni.

Many of the rest of the arguments apply to discussion websites in general. If you consider Wikipedia, for instance, scaling doesn't seem to be a problem. Taking Wikipedia is a good idea, since, despite what's been said, Quora is or should be a direct competitor to Wikipedia.

At a descriptive level, Quora isn't represented accurately.

Judging from the slant of the article, it seems the author is reacting to a bad experience on the site.