People have been trying to find ways to skip TV commercials for decades. It's going to be the same with ads. When it comes to our own personal devices, advertisers can't really win in the end. They're going to have to stick to things like billboards and other things put up in cities, but even those are being protested and banned in many places.
In theory, what about reddit can't be decentralized? All it stores is text and URLs to other content. There isn't all that much actual processing or computation going on, as far as I know, besides some rank calculation stuff. Am I wrong about this?
In that case, it comes down to figuring out how to pay the developers and some kind of election process for admins. But with a site with hundreds of millions of monthly active users, surely they'd be able to figure something out. Like each user who donates $10 or more gets a little perk.
And even without decentralization, micropayments and premium perks are already a much more promising model. Lots of people are buying reddit's silver/gold/platinum/a bunch of others awards. Tinder is free by default and manages to make loads of money without showing any ads. I don't think ads are going to be a sustainable model in 10, 20, 50 years from now. I think service providers are just going to have to figure out ways to provide value to users in exchange for money, like most "meatspace" companies do.