It would be nice to be able to switch search engines

I agree, as long as we can choose which search engines we want to include, rather than having a preset list.  For example, many people would want to use Wikipedia; I don't even want to have it listed because it isn't an academic resource.  Two different preferences, but they can be easily realized by a customizable selection.  Also, having a customizable selection would allow a person to utilize an uncommon search engine, such as Bible Gateway, Merriam-Webster, or Firefox Add-ons.  Many search engine add-ons have this feature.