Aaron Wall’s article covers the history of search engines from the very beginning. It is an interesting reading because it shows clearly the volatility of the SE world. There were times of very strong dominance by some players who did not survive because the did not innovate fast enough. The current SEO is based on the current type of SEs. Once they change (or once they fail to innovate), the current SEO will either have to change or will disappear.
The consequences for SEO: keep your eyes open and start changing today. Study new web technology trends (Yes, I mean technology trends, not just SEO news) and think regularly on what their impact may be on your work. SEO as we know it may dissapear within few years; the need to attract quality traffic to your websites is however permanent. I keep stressing to my (ex-)clients the need to think ahead today’s trends and dedicate at least 10% of their SEO budget on research (into social networks, personalized search future, viral marketing etc.) so that they are prepared when the changes hit.