The new drag-n-drop featre is in Windchill 10.2 now, but PTC is still ironing out some complexities with Internet Explorer, so it is not currently supported in IE. I understand the challenge this presents; PTC put a replacement solution in the product, but its not supported in the most widely used browser.
The current thinking is to remove the Upload/Download Java applets in the next major release (10.3) when PTC has full support for Internet Explorer.