"If Windows 7 share is dropping off a bit, those people could be moving to Linux, if they are individuals or businesses without specialist applications."
If a legacy Windows application doesn't need internet access to run then it won't show on these reports. Users will keep a legacy application PC (eg XP) off the internet as much as possible. It is then a moot point whether they will move their W7 browsing type activities to Linux until nearer the 2020 deadline.
No doubt many of us are looking at redeveloping home-brew Windows applications for Linux. It will offer a major advantage by giving us a chance to fix application problems - whose causes are currently Microsoft bugs that can't be circumvented.
An elderly acquaintance didn't want to give up his XP database, He was delighted to find he could preset the lan connection to "disabled" on that boot - while using only the W7 boot for internet activity.