Well, it looks like I would do something different.
For once I will continue the same model which Nadela had implemented, so Nadela stays there, I would only add a little something: A Mobile Strategic.
Mobile Strategic
I would build like 3 Phones, like great Nokia Phones.
The OS Would be Windows Mobile of course.
My expectations for these phones would be to fail but I will provide Support for the Next 3 years.
Every Year and a Half or so I will released an upgraded Phone Experience, I mean, New versions of these phones.
And the most important thing, I would create an app for every major service out there: Facebook, Instagram, Twitter, etc. And when I mean an App I'm talking about to create the best experience possible that can been bring to the end user with the allowance of the service owner.
When you think about these apps, think about that great app of IMDB when Microsoft released Windows Phone 7.5 years ago.
Then these apps should be differentiated from the one which can be found on Android and iOS. But the Microsoft Apps should be exactly the same but with better features.
This strategic should last at least for 10 Years. I would released companion hardware (for the cost) like Samsung Dex which will allow us to get into the enterprise segment.
So would be cheaper for a company to invest in a Windows Phone and a Dock instead of a whole computer or a laptop. Of course this would be exclusive available to companies which have a Microsoft contract.
So Microsoft would have an approach to consumers and the enterprise in place. Windows Mobile (I would change this name too, something which can be relatable or 'verbable' [Blackberry, Android, those are cool names]). Microsoft OS should be Closer than Android but more open than iOS.
As per investment this approach shouldn't be expensive as Microsoft it's continue developing the OS for Mobile devices, has continue to developing Mobile Apps (they're will have to add the new Apps teams but that shouldn't be expensive either), Microsoft has continue doing research and development of Mobile devices too, so shouldn't be expensive either. Thing about a One Plus One like company inside Microsoft with a Development team to build the great apps.
Everything else will arrive by itself. When people see how great Windows Mobile its, that every app they're need is there, that those apps are better than their counterparts from Android or iOS. That you can access all the services from Google, Facebook, Instagram, Twitter, etc without losing any functionality and even gaining some. When the enterprise see that Microsoft is really about long commitment and they hardware delivers and its cheaper because you already have a Microsoft Ecosystem in place (Exchange, Skype, Office 365, Windows, etc).
In essence that would be my approach.