Paywalls never will be the norm; I honestly don't think the Internet can support very many paywalled news sites.
I never liked this line of argument (what if X becomes the norm?) when applied to markets: if X becomes the norm, it will be because the market is demanding X more than anything else. If paywalls become the norm, then it will only be because consumers prefer content produced under a paywall model to content produced under a "free" model. But the friction of payment alone will prevent that from happening; so I don't think the free web is really in a lot of danger.
Now I do think a lot of paywalled sites try to have their cake and eat it too by posting their articles on news aggregators then presenting a paywall prompt. I think the news aggregators need to do a better job of blocking these types of attempts, but they won't because they're funded by advertising and I would assume paywalled sites are able to pay more to acquire traffic than ad-supported sites. This is the problem with any funding model where the money doesn't come from you: others' interests are represented above your own.
NYT is especially bad about using cookie and JavaScript tricks to allow spiders to grab their articles, but enforcing their paywall on users regardless. The Economist is a better example; when they post an article online, it's available to anyone for a period of time (3 months I think?), then it enters the archives behind the paywall. But there are many other paywalled articles that never get posted online, and they don't try to promote that content.
Also, I don't think there is a "perfect model". I think there are varied consumer preferences and that many models can be successful. There may be other models we haven't tried yet. But no one model is going to be universal, and if it is, it will be because the market actually wants it to be.