I should explain a bit what I meant by the factors I listed in my original post.
Rule #1 - Category: this would be separated into Power Currents, Currents, Recurrents and Golds. Each category would only be allowed so many songs in one sweep.
Rule #2 - Artist Separation: just what it says. Every artist would only be allowed to be played so many times within a given time frame.
Rule #3 - Tempo: this would be broken down into High Tempo, Uptempo, Medium, Downtempo and Light. This would also be restricted based on time between each track of the same tempo and would also serve to keep songs of two different tempo extremes from playing back-to-back.
Rule #4 - Genre: broken down into Pop, Rock, Rap, R&B, Dance, etc. Much like the category rule, each genre would only be allowed so many songs in one sweep.
Rule #5 - Artist Type: as was explained above, this would be broken down into males, females and groups. I wouldn't want to put too much restriction on my playlist based on this rule, but enough so that I don't get, say, 18 boy-band tracks in a single hour.
Hopefully that clears up what I was trying to propose. Does that make more sense? Does it make sense at all? ;D