We know that whomever this Hero of Ages is, they actually held the power of the Well of Ascension. I'm personally going to chalk this up as more evidence of it being Rashek, because it would explain how he messed up the world so bad. For example, he moved the planet closer to the sun, causing the burnlands and making the regions around the poles habitable. (Possibly so he could survive with a capital city right over the Well of Ascension.)
Now here's an interesting thought: what if there's a Well at each pole? If we have a ruin/preservation dichotomy, we could also have them separated on opposite sides of the world. This could also explain how Vin felt that thumping of the well; it was magnetic north. Furthermore, If miyabi is right, and TLR aligned with preservation, we could have an interesting yin/yang like, ruin-in-preservation and preservation-in-ruin thing; the power of preservation keeps ruin imprisoned while the power of ruin keeps preservation imprisoned. (or maybe I'm just making things overly complicated) However, we could also have a habitable landmass on the opposite side of the world. (though I'm inclined to believe that it would have been Ruin'd instead of Preservation'd)
And of course, if the mistborn world (we should start calling it Vinland or Elendland, in the fashion of Randland...wot readers get this) is on the pole (specifically, the north pole, as the Terris mountains were in the north originally) and if darxbane's theory is correct,
Yes. Imagine if TLR's death is causing the world to slowly return to it's original location? If everything he did was slowly unraveling? I have never looked forward to October like I have this year.
then we've got some migration to do. Of course, this would fulfill the whole green-world, blue-sky thing...
Of course, the major issue here is there's no answer to why the mist is kinda killing things...