I've got mixed feelings about the idea of bringing Marcelo to Juventus.
On the one hand, he's by far the best LB in the world in the post-Carlos era, and he'll likely maintain the same level for another couple of years.
On the other hand, if the left flank of Juventus looks like Marcelo - Ronaldo, it will definitely feel like a part of that successful Real Madrid within Juventus. I don't know, maybe it's only me, and it definitely sounds weird, but if Juventus wins UCL with them, it will feel like 30% of the title or so belongs to Real Madrid, and Juventus is just unable to win it without their courtesy of sharing with Juventus some of their players.
It's different with Ronaldo, since CR7 is CR7, he's always on his own. But CR7 + Marcelo probably would be too much and kind of bad for the "cogency" of the much anticipated European title.