There is a lot of content here that could be unpacked into a bigger framework. I liked the Solar/Shadow interaction and it would be interesting if that went further. I think the failure chances are going to create a real frog-in-the-well situation that doesn't fit the very evocative flavor text you've included. With a little tweaking I think they could have the players feeling they are "addicted" to their powers, trying not to be consumed by them, but this isn't quite what happens now.