Here's a couple of topic I would love to hear a show about:

1. The Rare Earth Hypothesis.
We hear a lot about the Drake equation and advocates that Earth is nothing special. But what about the other side which questions why extraterrestrial civilisations aren't obvious.
http://en.wikipedia.org/wiki/Rare_Earth_hypothesis

2. Solar System Formation.
This has been mentioned on shows but not a show dedicated to the topic. Before we started discovering exoplanets astronomers and physicists looked at our solar system and thought they understood how solar systems formed. Now we know that our system is unusual, and in particular that giant Jupiters tend to hug their stars.

I find this topic particularly fascinating as it shows us the limits of looking at one example and trying to generalise it. This is still the case when speculating about life elsewhere!

Would love to hear your thoughts on this topic.
:-)