In my opinion: no chance. As long as humans use search engines (like Google) to look for information online, that content will need to be optimized. A well-rounded approach to content development and optimization should actually benefit from Google Instant. More than SEO, it should impact how users search and find valuable information and/or the products and services they’re seeking. Good SEOs will adapt to any changes in searcher behavior that Google Instant brings about.
As for search rankings, Google specifically says that nothing’s changed :
The basics of Google search are the same, including how results are ranked and how Google determines relevant results.
Google Instant may also lead to higher impressions (in Google Webmaster Tools) for your web pages as they move in and out of Google’s search results as people type. For example, my U2 site may appear in the search results as a person types “u2 new” (as in “news” or “new album”), but it will disappear if that query becomes “u2 new zealand concerts.” Google has just published an explanation of how impressions will be counted with Google Instant :
1. The traditional count method – when your site is displayed in search results after a completed search
2. If the user begins to search and then clicks any link on the search results page, including an ad or “related search” suggestion
3. If the user stops typing and the search results appear for at least three seconds