This might have been a decent plan 10 years ago but now they made the OS core decent enough (and secure enough) that replacing the core is not really necessary.
"uphill struggle as the world passes them by" might just be a slight overstatement of MS problems. MS says they have 75% market share for x86 servers (I've no idea if that is a legit statistic). Macs are barely a blip in desktop/laptop market share. Win 8 and Win 8.1, which according to comments in posts like this is the worst OS since Win ME, each has greater market share than all versions of Mac OS combined.
They are obviously very weak on mobile (phone and tablet) but traditional desktops and servers are not being seriously threatened.