I think spiritual is a rather blank term. It doesn't have to mean Christian even though it usually does. There is a market for aethistic music but it has to be real. True beliefs I think will carry it in a song just like any other belief system. If you do though as a gimmick I think you will crash and burn. Most times gimmicks are just drawn from stereotypes and not personal exoerience and thought. If the person doing this type of writing has actually put some in depth thought and analysis into the subject I don't see why it wouldn't fit into any format. The aethist rapper thing is a little weird thought for me. I mean alot of modern music revolves around Non-Christian imagery and mentality so I don't see the shock value on that one. The same way I don't see any shock from Thor's Hammer. There is a big difference between shock and making a case for your belief. I listen to all kinds of music just about every style you can think of. I see this as a common theme in alot of styles. Sometimes it is aggresive and in your face but others it is subtle and you have to think about what they are saying. So I don't see why it wouldn't work.