The Techcrunch article itself can be ignored. The opinion is silly. But as a piece of evidence for the thesis: "the PR momentum has plateaued" it is serious, and part of a different problem.

PR is a funny thing. If you go long enough with exciting commentary with interesting developments that make the news in sufficiently controversial ways, you get written off as a newsmaker. This perception of non-growth or plateaued growth (as a company in company-space, not as a product in user mind-space) becomes a self-fulfilling prophecy. If a company isn't seen as evolving, new types of people (both users and employees) won't join, and the company won't be able to evolve.

If enough people say "Quora isn't doing anything" it's market positioning will get locked at the current unfavorable perception and it will be unable to do anything, no matter how clever and big the moves. New moves will be read as desperate attempts to get out of a dead end or pigeonhole (or worse, random R&D stunts) rather than part of a naturally evolving strategy narrative.

As a brand, you end up screaming "I am not dead yet!" but people have stopped listening.

Google actually had this problem for a while. For a company its size, for a long time, it wasn't keeping the vitality of the PR narrative strong and evolving. It looked like one mature product (search) and a bunch of other unrelated playpen experiments of varying degrees of technical success. The nadir was Google Wave. They finally revitalized the narrative with Google+ and the more recent Android developments.

I'd say the product itself is evolving fine. Kudos. But perhaps it is time to do more active PR, send tantalizing signals of big-league ambitions, etc.