So, here's the big question. What exactly is quality content? Besides relevance of subject, grammatically correct, formatted neatly, not obvious autospun garbage, etc etc, how will Google ever be able to judge a quality site or piece of content?
When you visit a site and read an article about a certain subject, 9 times out of 10 (unless it's some specific how-to, like how to change an alternator), the article is basically just a large opinion written in paragraph form. And that opinion isn't something that an algorithm can say 'this is quality' or 'this is stupid' or 'we'll rank you higher than the next site because my binary sensors agree with you'. An opinion can only be formulated, and agreed or disagreed with, by the human mind.
For sites like entertainment or e-commerce sites, it's still the people's opinion that determines whether it's the best store to buy from, or the best site to read about the celebrity gossip. A computer algorithm will never be able to determine the quality and popularity of the site by it's content alone. It needs people to tell them that, and the only way for people to tell them that is by:
a - counting the number of links
b - the relevance of where the links are coming from, and
c - the number of visits to that site via those links.
Of course, they need to keep their system running smoothly, constantly tweaking their algorithm to weed out the junk.. in essence, gigantic 'filters' to keep their system 'clean'. But this post isn't about how they count the links, or how they deem a link valuable or not, or how much.. its about the future existence of links, or people's popular 'votes'.
Even in the case of the factual how-to site, it's still the people's vote that "This is the best source about how to change your alternator in a 1998 Cadillac Seville". Two different how-to's could give basically the same direction, but the algorithm can't tell whether its a bright idea or not to remove the head gasket first. Only people (and their votes/links) can tell that.
Thats why they need to use links as the base ranking factor of their whole system. Because links are human 'votes' for agreeing or disagreeing with a usefulness of a site. Only humans can judge that, and that is what makes a page rank higher. The higher it is, the easier it is to find, the more people say "Google it" instead of "Yahoo it" or "Bing it" (because google gives you the right answer every time), and the more Google and their shareholders profit.
Just like any successful business, Google and it's system needs interactivity with people.. it can't just write a clever algorithm and keep it churning away on its own, letting the computer decide what is quality and what is not.. it needs people to help their system determine quality and relevance. That can only be gauged by links.
Even social signals can't do it without links. You don't see anyone tweeting or facebooking "Hey, theres this awesome website that I found, if you google 'car stereos', go to page 46, 6th link down, you click that and thats the page".. I suppose you could, but really you just put the link. That link is the signal, and if that link gets posted enough places by enough people, that site obviously goes higher.
Even if Google's algorithm evolves into some sort of Artificial Intelligence in the year 3629, it would then be ranking sites based on Google's 'opinion' of whether a site is relevant or not, and that would be only one of a million other 'opinions' as to whether a site is the most helpful and popular to it's users.
In conclusion to my post, which has now become a thesis, Google spends an enormous amount of time, money, and resources into determining whether the source of the links are in fact coming from real users. In the end, they want to deliver the most relevant results, for the people, by the people. That only proves the point that linking in itself isn't going away.
Google's entire business model is not necessarily based on fact, but based on popularity. People will always be their most significant determining factor, and the links they post are the headcount. The more people agree with the content on your site, the more 'it' figures your site is the most relevant and helpful, thus ranking it higher.. it's 'content' isn't better, per se, but it is more 'popular'. Just like politics, top spot goes to the popular vote.. the links are the ballots that the people cast.