Google has a leg up by virtue of the fact it could deploy any new product massively and immediately, but that barrier to entry is hardly insurmountable. It just means the new paradigm would have to be significantly better than the current one, for the following three groups:
1) Advertisers. Companies would need to see a significant benefit to moving to the new platform.
2) Site owners. Either by virtue of UI or increased revenue, a new platform would have to offer a significant advantage to site owners to spur adoption.
3) Users. This one's basically optional, and included in 2). A new advertising platform would have to be unobtrusive enough to not piss off users drastically more than current ads, but a strong enough showing in 1 & 2 would make that less important. Ideally, a new platform would offer ads that users want to see, by virtue of being either entertaining, relevant, or both. See movie previews in theatres for a good example of this.
1) Advertisers. Companies would need to see a significant benefit to moving to the new platform.
2) Site owners. Either by virtue of UI or increased revenue, a new platform would have to offer a significant advantage to site owners to spur adoption.
3) Users. This one's basically optional, and included in 2). A new advertising platform would have to be unobtrusive enough to not piss off users drastically more than current ads, but a strong enough showing in 1 & 2 would make that less important. Ideally, a new platform would offer ads that users want to see, by virtue of being either entertaining, relevant, or both. See movie previews in theatres for a good example of this.