SEO as a zero sum game is by definition dead,
One search engine and one top position for each term implies that to be number one, you have to push someone to number two. This action alone is against the foundation of internet, the spirit and soul that gave life and made the web such an amazing place of cohesion, inspiration and sharing.
Google to be meaningful and being a goto solution is trying to contextualize it’s results as much as it can, by getting to know you ever better, by listening to the social stream, to the time of day and hundreds of other parameters, and it is already presenting different results for the same search term, based on what it knows about you.
Eventually the number one position for the same search term WILL BE INDIVIDUAL and totally personal.
SEO becomes therefore ever more a global solution that has to deliver the best meaning for a wide range of situations.