I think mobile is something that will have a top 3 position on this. Either the options will develop so much, or the existent engines will change because of the most users, i don't know. But something will include mobiles too..we are to addicted to them..
Future of Search engine is bright and so stunning. A huge number of people search through engine of all kind but google is best search engine all the time.
Search engines will be used as same with advanced algorithms which will not give rank to websites which use black hat SEO to come up. Good quality websites will get top position.