I don't have a DK with the chest to verify this works, please PM/mention me here or on Discord @ Dan#8152 if it's broken.
Version 4 (latest) now loads for Frost and Unholy.
Tracks Cold Heart ( http://www.wowhead.com/item=151796/cold-heart ) stacks.
v1 - Lights up when Pillar of Frost <=3s.
v2 - v1 and if stacks >= 10.
v3 - v2 and only loads for Frost DK.
v4 - v3 and now loads for Frost or Unholy DK.