Sprawler's wings are simple. His patron god, the Judgement, has decided he's powerful enough for them 
my friend Cryo had the best idea ever. A simple explanation for suddenly spawning wings.
/em RedBull
To be honest, I've had a hard time justifying them for ANY of my characters. So far I've got one demon possessed brute who will be having them as a pure cosmetic (he can't fly). And I guess I'll slap them on my peacebringer just so I can watch them work with SOMEONE.
Oh, and those at GG had better watch out for the appearance of the unbearably smug GenericWingedHero142 who will most probably show up, annoy the hell out of people for 15 mins with his aura of self importance, then shove off, never to be seen again.
The heroic cannot be the common, nor the common the heroic.
- Ralph Waldo Emerson
well all I could think of is for the Mutant origin:
humans are evolving into winged superbeings, bout it really.
Idunn is growing into her powers slowly (which are divine in nature from norse mythology) and the wings come when she attains valkyrie-like status. They just kind of... flourish to life. Flying is definately something associated with valkyries, so that's pretty much that.
My stone armor brute won't have them though, considering she can't fly and if you can't they just... sit there looking awkwardly inanimate. So I'm weaving that into her story, and that she's quite annoyed to be part of the wingless type of demons. 
In the case of Serafine, considering that her appearance is the result of her magically trying to get herself back to normal, we can safely assume that wings or any other non-baseline human physical characteristic is the result of typo or a distraction.
(She still can't get the ears right)
In your dreams, I'll still be there with all the days that never came.
And I'll be just a story.
That's ok, we're all stories in the end...
Speaking of a Valkyrie, does anyone know if existing NPC heroes will spawn wings? I think I've seen some demon-winged villains and trenchcoat 'detectives' on Test. I'd quite fancy seeing someone like Valkyrie produce large feathered wings where she stands in Steel Canyon. Positron'll be like "darling, those look fabulous" 
So many veteran mutants 'mutating' wings and more suddenly appearing onto the scene... some viral catalyst?