Thanks for your feedback.
The change you have found is purposely made by us due to Cordova incompatibility to parse this path for some of its APIs because of the second colon in the path. After we successfully expanded the File API support to its full volume in the Simulator we had to bypass this limitation by introducing this constant which replaces the root folder path. This does not change anything on actual device behavior so you don't have to worry for any consequences.
Is there any particular reason to use Filesystem.root.fullPath value?
Share what you think about AppBuilder and Telerik Platform with us in our feedback portal, so we can become even better!