did they ever really explain that bit about why their was a ancient energon cauldron/smelter buried in the earth in the arctic during the sunstorm storyline? and what does that energon cauldron have to do with unicron ? did it serve as a prison for unicron's disimbodied spark?
As Dreamwave went under, no, we didn't get any answers to the many dangling mysteries of the ongoing.
My guess is that they were working towards a story about Earth being prepared to be be terraformed into a new Cybertron and for some reason, the plans went awry. Maybe Sunstorm knew about from Memories he received from Starscream and was going to go finish the job, or possibly, Earth was a prison planet for the Decepticons and Straxus was smelting down Cybertronians there. Someone should ask the writers.
It really bothered me that we never got an answer to that. It was the biggest mystery from the Sunstorm saga and then they completely dropped it and never picked it up again. I'm also annoyed that we never got a Sunstorm Saga TPB.
It might not necessarily have been Sunstorm who was interested in that location, but The Fallen, who was inside Sunstorm's mind at the time. Furman wrote a script for an unpublished story that would have brought The Fallen into the main series and linked The War Within with the main series at the same time. Given the billing that "Optimus and Megatron would be the focus in a story that takes the fight right to Unicron", probably Jet-Fallen would have used it to summon Unicron Earthwards? It's a shame we'll never know how that plot would have gone. As overused as Unicron was back then, there was definite potential for something very interesting in there.