Persona was launched in July 2011. It has gotten a fair amount of publicity in that time. Yet the adoption rates among websites and users are still very, very low.
I just don't think that there's any significant demand for this product, realized or unrealized. People know about it, and people could choose to use it, but doing so would likely not make them sufficiently better off.
Maybe that's not ideal, from an ideological standpoint or when it comes to "openness". But I think it is the, perhaps unfortunate, reality. It really doesn't make sense to endlessly waste resources on a product that has been proven to be unwanted, or at least not valuable enough to use.
