Books are already pretty much pay for. The "problem" with the TV model is that it's "free," and must be supplemented with ads to make money. Since it's fairly accepted that you pay for books on a per book basis, I don't think this becomes a problem here unless there are a bunch of people out there who would prefer it that way. I don't know anyone who would rather sit through commercials in their book rather than buy it, own it and read it whenever, but it's not outside the real of possibility that it could happen, I suppose.
The biggest reason I don't see this happen though is that libraries exist. I see no reason for them to go away, since they are paid for by tax dollars and those kinds of institutions are rather difficult to remove. Most big libraries have big e-book "sections" now, so even for those who don't want to pay for the book, I don't see ads in their future.