The last 40 years have shown us that 3 types of music will always be popular. Rock, Hip Hop/Rap and the pop music of the moment(whatever its defined as). Over the last 40 years, while one is usually popular the other usually lurk around with the occasional hit. At the moment bubblegum pop or whatever is most popular, hip hop(ganster rap, will Smith ect.) and rock(Nu Metal, Pop-punk ect.) are still thereabouts. Think of all the big music revolutions (Nirvana, The British Invasion ect.) have all involved these 3 types of music. There will be some kind of new revlution soon, probably rock as it is the least popular at the moment, it mightnt be as big as Nirvana but so what) People always get bored and look for new trends.