To reach everyone under 25 that's only substantial impression of U2 is an unwanted album on their phone.
Think about it. For younger people born 1990-2000, how many new U2 songs do they really know from their lifetime? Beautiful Day and Vertigo are the biggest two but each are 12-16 years old at this point. Collaborating with someone like Kygo is a clever way to get their music into the ears of younger listeners. TBT is quite the earworm and it could help shape a positive opinion and get people interested in the band before the SOE rollout begins (if ever..).
U2's only hope for staying relevant and staving off the Dinosaur Band critiques (which have been ramping up lately) is to keep younger people interested in their music. This could be one way of doing that.
Agreed, there's potential in that theory, but what would be the point if there is no album follow up available quickly? Could be easy to grab attention, more difficult to hold that for 4 or5 months til SOE comes out in the spring of 2017, or worse!!