The current documentation has a place holder for this in the readyStateChanged event but is labled TBD.
http://msdn.microsoft.com/en-us/library/windows/apps/br211840.aspx
If this was implemented in the DeveloperPreview then you could probably us this. I do not know if or when this will be enabled for future versions.
I did find in the debugger that you could use the _viewport however. Although this is not currently documented, this might be a good workaround for you. You can get the listview control's _viewport member and add a scroll event
listener. You can compare the position of the scroll then with the listView ScrollPosition.
-Jeff
Jeff Sanders (MSFT)