With regards to U2 ever becoming "cool" again, I think that ship has sailed. The time for that was around 2009 or so, but the band was too focused on being seen as modern and relevant - see the abomination that was I'll Go Crazy If I Don't Go Crazy Tonight live. Bruce Springsteen, Fleetwood Mac, Elton John, Billy Joel - all of these acts just kept being themselves and let the culture rediscover them. They didn't chase it. Even bands like Creed, Limp Bizkit, and Nickelback, the easy targets of the last two decades, are seeing legit career resurgences.
U2 didn't do that - they went the Ryan Tedder route. And Bono just seems a little too try-hard. Which is not to say I care about any of that shit - I don't care if they're seen as cool by young people. I just think that opportunity has passed.