Just a heads up: Not sure where yall are getting that MotE is a combination of boots and 2pc, but this is the details for the talent:
"Casting Lava Burst increases the damage of your next Nature or Frost spell by 20%."
There's no cooldown, and it triggers on cast completion (not damage); it's pretty similar to our current 2pc (although things like EB and LB can consume it).