I'll tell you what- if they do decide to bring a POP song back, they need to give it the Ultraviolet treatment. They need to go full force and make it stand out. It needs to grab you by the balls- light show, Bono singing and really selling it, etc..
The recurring theme in the popularity of the hits of the last decade are that when the songs are played live, Bono sells it. He's in the emotion. He's singing, jumping, playing, dramatizing.
In my opinion the the biggest reason POP and NLOTH were relative commercial let downs was that the songs didn't really lend themselves to the theatrics. Or, they made a conscious effort not to pull much theatrics. Most songs were sung pretty straightforward from the stage.
Ultraviolet is a pretty obscure song- you don't know it unless you're a committed fan. Same for Unforgettable Fire. (I don't know if it was big when it came out but it falls in the same obscure category as Ultraviolet now).
Ultraviolet got the "works". Awesome lighting, light jacket, steering wheel, band playing the shit out of it while Bono sold it.
UF just got a cool screen effect. No theatrics. Nothing selling it like UV.
UV stayed for almost a whole tour and got rave reviews. UF quietly disappeared.
If they play a song from POP I think Please could kick some ass as it did on POPMART. None of this acoustic stuff!