I'm not sure it's necessarily correct to think about life and death in terms of purity and corruption. Death is natural, it is part of the cycle. They go hand-in-hand. If Eonar saw fit to empower a Watcher with command over Life, perhaps it would only be natural to do the same with Death. And Odyn is a dick, but Valhalla is righteous. Death is not purely evil or corrupt.
Maybe they could play with the idea of Freya and Frigg being one and the same, though. That could be interesting. Mirror selves watching over Life and Death or something.
And if Icecrown is a gate to the Shadowlands, that gate surely predates the Lich King being hurled into Azeroth by Kil'jaeden...
Come to think of it, Eonar championed the cause of protecting Azeorth, believing she was key to fighting the Void Lords.
And she now dwells on the world Elunaria? There are a lot of links between all these themes, with Freya kind of at the center.
I'm just spitballing here, though.