Originally Posted by
SweetRein
The concept is neat, however, I wouldn't carry it further than a novel.
Setting a significant personal cost causes the issue of a player being unable (or too paranoid and thus unable) to use their class abilities. A player doesn't choose to be a magic user to shoot a crossbow.
Really, I've always been of the opinion that magic should be less tolling, more consistent, and weaker. Also, more subtle.
It also must be mentioned that who is playing matters/what is being played. A life force draining mage might make a great BBEG - giving the interesting effect of the witches in Stardust - but it's not so interesting for a player.