What does the term 'art song' even mean. Art is not constrained. A song is a song. Reproduction of historical styles has some interest, but why study past songs when you can just sing and make up your own songs to your own styles and rhythmns.

Today I sang to my neighbours cat as it shaded in my garden, it is so frightened of hands because it gets mishandled by the children in the house in which it lodges. So I cannot even pet it without it having an anxiety attack.

I tried to soothe it with a quiet song that went along the lines of ," sorry cat, you're safe here, you are welcome and I will not mistreat you" The tune was whatever it happened to be at the time, it is not written down, archived, reproducable - it was just as it was then. Lost and gone forever.