This is pure opinion, based off of observations. So keep that in mind as you prep your flamethrowers...
Metal and Rock are still doing just fine... outside of America. It's thriving with bands like Powerwolf, Orden Ogan, Accept, Edguy, Nightwish, and the many other bands that fall under various "power," "thrash," "symphonic," etc. monikers from other countries. The problem is, that in America, unless a given foreign band has been around for a good while, or comes to the U.S. a lot, many of those bands don't have the name recognition to carry them around in the U.S. and garner them attention (outside of labels like Napalm Records at least). Sure, there are bands like Iron Maiden, AD/DC and Accept that get noticed when they come to the U.S., but they don't really draw in droves of new fans. Instead, they get by mostly with those who have been listening to them for years (or decades).
Now granted, we 'muricans have a few of our own Rock and Metal bands. Metallica, KISS, Megadeth, Van Halen, Anthrax, Rob Zombie, Alice Cooper and others who do well when they tour. But they're familiar names that draw in the same fans again and again, while slowly pulling in new ones. And though it may not seem like it, these bands are still inspiring people to join the Rock 'N Roll fray. YouTube's copious amount of young electric guitar players shows that the idea of being a rocker is still out there, but you have to remember that the term "rock star" isn't just about playing Rock or Metal. It's the idea of being on stage, in front of thousands of people that are watching you perform, hearing you sing/speak, and getting whatever message you're putting forth. And while there are new faces coming into the world of Rock and Metal, more faces seem to be headed into other genres to find that "rock star" life. There has to be a reason for this, right? A cause of some kind that's making certain genres more attractive to young musicians.
Well, think about it. We live in a world of "I want it NOW!" People expect instant results, and want to put in as little effort as they can get away with. With that in mind, here's a quick question. What genres generally require you to be able to play an instrument? Country, Rock/Metal, Classical, Folk, and their ilk that involves guitars, drums, pianos, violins, flutes, various brass instruments, etc. What genres generally don't require this? Pop, Rap, the various slices of Electronica, etc., as what you write musically can be done electronically. It's become pretty easy to write out a few beats on a DAW, put some lyrics to them (or just go instrumental), and then put it out there. Yes, you still need a sense of timing, rhythm, rhyming, harmonies and so forth, but you don't have to know how to play a real-life keyboard, guitar, violin, drum set, or anything to create a complete song in that second group of genres. The sheer number of programs that are out there nowadays that allow this to be done is insane. As a result, that second group of genres I listed leave the proverbial door open more, so you've got more people trying to step through that door instead of trying to invest the time in learning to play an instrument that you have to hold and touch.
I know what you're thinking, and yes, I know that sounds a touch mean and simplistic. But it's also the generalized truth. I'm a living example of it. I can't play any physical instrument to a degree that I'd be able to perform live on a stage, but that doesn't mean I don't have ideas, or the ability to look up what the limitations are on a given instrument so I can represent it more realistically. My remixes over the years show this growth, and my upcoming album will as well. I can't play live, but I can do research and compose, and that's where genres like Rap, Pop, R&B, Electronica and them are more open to people like me. Hell, piano and classical music (my main areas) are fast approaching the same openness now thanks to very realistic VSTs and sample sets, but they still have expected limits that need to be taken into consideration in terms of what the real instrument can and can't do. Pop, Rap, Electronica and them don't have that caveat. Is this a good thing? I don't know, to be honest. It could result in a huge flood of mediocrity and shit, with droves of forgettable, horrid albums and songs. But then again, being able to play an instrument live never stopped that from happening, did it? Lots of other bands came and went over the last 50 years alone that no one knows about, or even remembers these days (assuming anyone did back then).
So yeah. To me, the "rock star" isn't going extinct, it's changing because the music industry, and what it takes to make music, is changing. We still have people wanting the so-called rock star life, but "rock star" isn't about Rock or Metal. Never was. It was just a term to attach to the idea of commanding an audience and getting lots of cash, which can be done in pretty much all genres. Elton John did it, so did Liberace, Kenny Rogers, The Pointer Sisters, and many others. But the older genres of Rock, Country, Classical, and those genres have steep learning curves that extend over many years thanks to their greater need to learn to play real instruments, where as Rap, Pop, R&B, Electronica and them have less intimidating learning curves that make people think it can be conquered in less time. So, given the "I want it NOW!" mentality and short attention spans that exist in the world today, more new artists are going that second group of genres. Some will make it because they have a real talent in them despite the lack of live playing skills, and others will fade away without being noticed because they're as generic and uninteresting as can be. Hopefully, I wont fall into the latter group
Edit: Smoothed out a few thoughts.