Remixing the search results might be the answer for a better search engine. SearchMash, Google's playground, has been updated and now includes results from blog search and video search, which are displayed on-demand in the right sidebar. Now when you choose to see the results from a certain type of search, you can still view the top results from the other search types.
While Google's experiments are interesting, I think a better idea would be to integrate other search flavors into the main index and enable them if the query is appropriate.