first of all sorry for my english its not the best at all. So i want to share my opinion with you:
How about a feature which allows you to set up different categories inside your playlist like "Blue", "Red" "Yellow" ...
which got customizable playing rates.
So i got 80 Songs and there are about 5 songs which are absolutly awesome and i would like to hear them quite often, but not on replay at all. So i put them in the group "Blue" and just give this group a playing rate of 80% so my favorites will be played a bit more.
So i could set up my different groups from "awesome" to "not bad" and could control the behaviour of these groups.
This is sure easy to make with about 2-3 configurations sites and a slidebar? for the percentage configuration of the different groups and a color menue.