So I was a victim of the recent developer preview infinite loop with my Samsung ATIV S. Was forced to flash back to WP8.. So now I've updated officially back up to WP8.1 Update and lo and behold Xbox Music now shows artist pic on lock screen... Well what-do-ya-know.. It still only applies when playing tracks streaming from Xbox Music service and not locally stored files... but still.... It actually works now.. This never worked before... Guess there's a silver lining in the mess.