CapriUni

This is a good mental exercise but I think you are making it to complex. In fact I completly disagree with this statement.

"Like elephants, some ideas are too big to fit a single metaphor. But can those ideas be put into a song, where language is kept to its bare bone minimum (Songs must say things even more succinctly than poems), without thouroughly confusing the listener?"

Ideas buy their definition, can be stated succinctly. What a song does is wrap emotion around the idea. I say. Show me an idea too big for a song and I'll show you a poorly formulated idea. Which makes the answer to the question below a simple.."No"

Are there some ideas that just cannot be sung about?

I actually think any of us would find it difficult to find an idea that hasn't been sung about and added to popular culture in that way. In fact when a new idea is found and executed well in song it often has enough novelty to become a hit.