I think he'd be a good option although he'd have to walk away from the chance to take Spain to a World Cup should United want to replace Ole Gunnar Solskjaer with 'Lucho' before next year's World Cup.If it does go belly up for Ole and he gets sacked this season what about Luis Enrique?
Erik Ten Haag and Zinedine Zidane are other people worth considering. Ten Haag's style of play is impressive. Although that would come with another stylistic shift for United. Zidane might just fit United's squad a bit better. Does Zidane have his heart set on managing the French national team after the next World Cup though?