"Most Relevant Band In The World"
Honestly, I'm very curious as to what you mean by that..."Most Relevant Band in the World"...and how that is something you can possibly evaluate or examine enough to make it certain. This word "relevant" seems to be thrown around way too often here. What the fuck does it mean? Influence? Historical standing? Record sales? Media coverage? TV appearances? Critical success? Public image? Strength of material?
Do bands get "relevancy" points whenever they play a great gig? A relevancy point magically flies off of a guitarist's fret board whenever he hits a particularly poignant chord? The singer gets an automatic PLUS TEN relevancy boost when he delivers on SNL or Letterman? Or does he get the boost when a different successful band mentions him? How are you determining this?
I don't think it's possible for U2 to be 'relevant' in the sense that their music is played on MTV, top-40 radio, etc. Pop music is now so drastically shifted towards younger audiences and hip-hop/dance/pop/very poppy rock acts (i.e. Maroon 5)/syrupy country like Taylor Swift/etc. that it's impossible for a band of 50-something guys playing rock music to crack into that consciousness. In today's popular music world, Jay-Z is the elder statesman...and he's 41! I'd say that Madonna is the elder stateswoman but she doesn't seem to make music anymore. This isn't to say that today's music is all crap; for example, Kanye West's last solo record was phenomenal and probably the most 'important' record of the last few years and it was a huge hit. I'm just saying that modern music has changed enough now that U2 are simply 'too old' for the current zeitgeist. Like, you cited appearing on SNL and Letterman.....those venues in and of themselves are dated. (That is, unless, U2 brought some of their stagecraft to an SNL performance. To use Kanye again as an example, his performance on the show in September 2010 was mindblowing. Artists are readily allowed to go nuts with their performances on SNL now, so U2 should really try something visually wild if/when they do the show again.)
The fact that U2 lasted at the top of the 'biggest band in the world' for as long as they did is stunning and will probably never be matched by any musical act. From the mid-80's to the Achtung Baby era, surviving a rocky stretch with Popmart to hit it big with Beautiful Day, and then to follow that up with Vertigo and the brilliant iPod tie-in (which was an ingenious way to keep fresh). That's over 20 years holding the title.
I'd love to see the next U2 album just be entirely focused on a musical concept and not have stuff like Crazy Tonight/Boots/Stand Up Comedy shuffled into the record just to chase some nebulous 'hits.' In this day and age, a band is far more likely to achieve a hit with an inventive YouTube video or viral performance than they are with a conventional-sounding radio single, so U2 should explore that route.
And, the idea of aping the Stones for a stadiums/arenas/theatres tour is AWESOME. I would line up to tickets for all three shows in my town. Seeing U2 at the Rogers Centre with 50,000 other people, then seeing them amidst 18.000 at the ACC, then amongst, I dunno, 1500 people at Roy Thomson Hall? Good lord, that would be incredible. Those theatre shows would be the hottest tickets in any town.