CMD+Shift+4 has always allowed you to take screenshots of any parts of your screen, (including your devtools), so curious why this is a feature in Chrome? Unless it's meant for Windows maybe where it's harder to take screenshots?
Anyway, why would it be harder to take screenshots in Windows? Have they restricted the Win32 API recently (I haven't kept tabs)?
Since Vista, there is also snipping tool, which allows the same things as Mac screenshoting.
I could imagine it would be useful in remote debugging sessions (such as when inspecting android webviews over USB).
For the record, it's still not a region selector but there is also alt + printscreen to take only the visible windows.
Apparently, Windows 10 Creators Update comes with a shortcut to capture a region, Ctrl + Shift + S.
http://www.thewindowsclub.com/snipping-tool-capture-screensh...
For the record, cmd+shift+3 takes a screenshot and immediately saves it to your desktop on macOS.