This isn't a Smart Playlist but I still think it's an okay idea:
Choose one song from all the songs by artists starting with 'A' and put it in a new normal playlist. Add a song from all the songs by artists starting with 'B' and so on through the whole alphabet. Make them as diverse or as similar as you like (eg. Rock songs A to Z). Alternatively, you could choose songs that have the letter 'A' in the title, 'B', etc.