This is, if true, a very interesting situation.
I think we're on a position similar to Arsenal the year they signed Özil. Was an AM their main objective? No, they already had Cazorla ans probably Arteta and Rosicky as backups. Did they got him? Yes. Do they regret it? I don't think so. They found him a way into the lineup and he improved substantially the quality of their starting XI. He was an opportunity of adding WC quality to their team, they took it.
Alex Sandro, as the Brazilian crew states, seems to be a very well rounded LB, WC even.
I'm one of the many that only see Asamoah as a LB now, due to how our squad is composed. But I gotta say that if getting Alex Sandro is within our possibilities, I think we must take him. We may don't need him now, but we will, next year Evra will most probably be gone. And then there's the prospect of Pogba leaving the same summer. I think that opens up a space in the squad, since Asamoah could be moven up to the midfield, we'd be left without a LB in this case scenario.
For me we gotta make this happen if it's true, Llorente + €10-15M would be a sweat deal for a 24yo WC LB.