> Could AaaS (Adblock as a service) be a viable business? I think I'd pay for it.
It probably could, however I'm sure it would be shut down quickly by advertisers and parties showing ads - after all, you're offering a service to remove their source of income. Unless you'd funnel part of your subscriber's income back to the advertisers, based on whose ads you block. But I'm sure it'd end up being too expensive for the consumer and too much of a hassle for the one offering the service.
Not to mention you'd force your users to funnel all of their internet traffic through your servers, and it wouldn't work with encrypted pages (which large parts of the internet is moving towards)
Privoxy - http://www.privoxy.org/ does just this and works very well when configured properly. It's also one of the few ways to reliably block ads on iOS apps.
You do have some information in the browser you can't get to from the outside. For example, the filter with the most hits for me is "@@||192.168.$xmlhttprequest", which whitelists XMLHttpRequests to 192.168.*. A proxy can't really tell the source of a HTTP request. But that kind of thing is sometimes the only indicator telling the difference between an ad and useful content.
There used to be a proxy adblocker that did that, but I don't think it works anymore.
The Kindle browser uses a proxy to pre-render pages on the server in order to lighten the load of the device.
Could AaaS (Adblock as a service) be a viable business? I think I'd pay for it.