That's what Experts Exchange was doing. Back in the days before Stack Overflow, EE was one of the hot places to go for answers to software engineering problems. It was a free site for many years, then one day they decided to require a subscription to read the answers. Google still indexed the question, so that you would open up a EE link, only to be greeted with "the answer requires a subscription". Google allowed that for a number of years before finally deindexing their results, but it took bloody forever!