Brad posted this in 2010, not sure its still relevant in FE .. but it does paint a very drifferent picture than the Sion that are in the game now, I want Sion to be rare, powerful and very dangerous.

"There are also the Sions but they’re not a race as much as, well, children of the sovereigns. The sovereigns are channelers but their children aren’t.  Channelers have a very long life (hundreds of years – they’re effectively immortal in our game but they’re not truly immortal). Their children have a normal life."

Original Post by Brad

This is the picture Brad posted to depict a Sion .. looks like a Wildling to me, but perhaps they share something in common

Nym in the book was a Sion, he was a major character and was playable as a Sov in WoM.  We was the fastest character in the game.  We was exceptionally fast, all but impossible to hit and a skilled warrior.  That pic really doesn't describe what the book had as a Sion to me.  Although I believe in Elemental, a Sion is someone who has a special gift that isn't magic.  They are not channelers, but are gifted in some mystical way to be a bad ass.  

I think Nym looked more like a tall, strong Wraith with white hair.  Those pics look like wildlings to me.