I'd rather hear Bono work with "has-beens" who are still remembered and (for the most part) respected for their contribution to the world of music than the talentless flavor of the week that no one will remember in twenty years. Santana's recent albums are going to feel very dated in that much time.
In any case, I don't think they should do any duets as marketing decisions or anything silly like that. They should work with artists they respect, old or new. I'm sure there are a lot of current artists who will still be respected decades into the future, but they're probably not the ones that make the guaranteed hits.