I really want Zidane, for multiple reasons. First and foremost he commands a lot of respect both as a legendary player and as a successful manager at a big club. He also has a good relationship with both Ronaldo and Pogba. The team has to be built to suit Ronaldo's strengths, and I think Zidane can finally unlock Pogba's true potential by motivating him & coaching him in a system that accounts for his strengths and weaknesses. I also think he'll make it easier to attract quality players from other leagues.
Another reason I wanted to bring him in overlaps with how I'd like to see the team line up. At Real he used a 4-3-3 that featured Casemiro at CDM, Kroos, and Modric, with Isco coming in to alternate or serve as the number 10 in a 4-2-3-1, which we've done with Bruno and 2 midfielders. Ronaldo also became more of a striker during this time alongside Benzema, and if we could find a way to effectively play both him and Cavani, it would be awesome.
I want to experiment with a 4-3-3 because Bruno and Pogba can play in the same team and drill patterns of play that break teams down, something that's proved challenging for United for years. It's risky given the defensive mistakes we've had, but with better coaching I think it's possible. In a 4-3-3 we'd need a specialist CDM, but for the time being, I think Van De Beek could potentially play there, with Matic backing him up (and in emergencies, Fred) until a specialist is brought in. (If not, a midfield 2 with Matic/VBD and Pogba would at least be functional.)
Another problem Zidane could solve is our defensive lapses, specifically the wingback issue. Shaw and Wan Bissaka are constantly out of position, which in turn creates chaos for the centrebacks as they don't know who to mark. Marcelo used to play an extremely attacking style and Carvajal joined the attack as well, yet the team managed to maintain control in difficult games. I also think that Zidane would commit to his wingers and focus on crosses, which are essential for Ronaldo & an effective attacking strategy overall.