People go to google because they find what they're looking for: excellent search results.
That's google's business. Most major companies and websites have their sites built on .com domains, so those are likely the most "relevant" sites. If google all of a sudden starts ranking other extensions higher rather than ranking primarily by relevance, people are going to use other search engines to find what they're looking for. Remember, this is why we switched from yahoo to google. Nothing is stopping us from switching back if yahoo or bing would return more relevant searches. Google understands what their business is, and won't make any risky decisions like this. They may promote other extensions to combat cybersquatting and give other options, but unless the major entities move away from .coms, they will remain KING. Google will likely tweak their algorithm, but a company that's built on good search results will likely not make any major changes.
I actually see new extensions helping out the .coms b/c it can bring new investors into this field. The majority of people still don't understand much about domains, extensions, websites, etc. Massive marketing for the new gilds can change that- I wouldn't be surprised seeing new heights for .com sales. Imagine 5 times the amount of investors, 10 times, etc. This can exponentially drive up the prices of domain sales in the most valuable, most in-demand extension. You won't see me selling my .coms any time soon.