For adventures, and some types of supplemental material, I don't mind a periodical format.
However, for core rulebooks, I think it'd be a bust. Mostly because advertising is ephemeral - it deals with the things available right now, because a large part of most product sales are made within the first few months after release. But my core rulebooks are supposed to last me many years. The ads in the book when I buy it will quickly become irrelevant, and thus an annoyance to me as I use the book three years down the line.
However, for core rulebooks, I think it'd be a bust. Mostly because advertising is ephemeral - it deals with the things available right now, because a large part of most product sales are made within the first few months after release. But my core rulebooks are supposed to last me many years. The ads in the book when I buy it will quickly become irrelevant, and thus an annoyance to me as I use the book three years down the line.