Isn't Windows 10 meant to be a unified OS platform
I mean, The core of this is not just for your average desktop, but for tablets of all shapes and sizes, for Windows Phones, and for their server class O/S's.
Doesn't every android / Apple / Windows phone already support some level of predictive typing and auto-correct features to make your user experience with small screens and sausage fingers a little less painful.
This is already common in many platforms that are used by millions, to see it on the desktop is a surprise, but should not be unexpected for a test release.
There will be different components that will be provided around the core O/S and some will be used on tablets, whereas others will be available on server platforms.