I would love to see that. Give him the resources and look what he can do. His record is exemplary. Porto, Chelsea, Inter, and now RM (League pretty much bagged and strong contenders for CL)
He could turn Man City into Englands best force, by a long shot.
Porto, relatively one league team, Chelsea, were second before he joined AND Arsenal got worse the next year, Inter, were first before he joined with all the main title rivals having been punished and set back for years, it was also a one team league till they recovered, Real.... Real/Barca tend to go through spells at the top and again most people will point out, he got 3 LESS points in his first year than Real had the year before, and Real have spent epic amounts to regain the title in the past 3 years.
The thing Mourinho has done better than anyone else is move at the right time.
ANY half decent manager moving to Chelsea would have won the title, and the team were definitely getting worse under his helm before he left, ANY manager would have won with Inter while he was there. Best team, rivals with points docked or relegated. Champs league I'll give him, that was impressive, though it took an unprescedented "anti football" campaign to win it and a lot of luck. I think most managers would be doing exactly as well as Real in the league this year also. THe lead was almost exclusively established by Barca being 10-13 points worse off when the lead was at its biggest, NOT Real being 10points better off than the previous season.
Real have bought, to buy the title back, Ronaldo 80mil, Kaka 60mil, Alonso/Benzema/Coentrao/Di Maria 30mil, Khedira/Ozil/Albiol 15mil, Carvalho/Surih/Varane 10mil, Granero/Arbeloa/Callejon 4mil , Adebayor was a 3-4mil loan fee, Altintop on a free and Pedro leon for 8mil who was sold on a free a year later.
So, £350mil give or take, on top of the squad they already had, and the team being ahead in the league is STILL more about Barca getting worse.
As with Chelsea who made massive gains in the league in terms of moving from 4-6th up to a solid 2nd BEFORE he joined, Real had a couple bad years and some low points finishes but spent and were only 3 points behind Barca when he joined.
I've yet to see him take a team, build it up, change it completely, and make a significant change in league position. Can he take over say, Liverpool, or Arsenal and buy/play/train/change the team and make them title winners? I don't know, maybe he can, he's never had to.