perhaps, if a person were to create a topic and it get over 100 replies in like 3 days or something, (very unlikely but probly has happened a time or two, i think they should get like 10 ap. this probably sounds ignorant, but i like this thought.
The thing about this, is that it does not actually reflect the quality of the thread in question. That is why I would be hesitant to implement a system such as this.