"I'm afraid I might end up with a poem rather than a song."

You could pinch a traditional melody you know and work the song round that? I think that's pretty much what many of the old broadsheet ballad writers used to do.

But it's a good question, what features make a traditional song sound traditional? And how do people currently writing in the traditional idiom go about composing new unaccompanied songs?

I think there's quite a lot of potential scope for contemporary unaccompanied songs, particularly as song cycles for small theatre productions.