To be able to chose the font and styling of the Code window.

I hate reading fixed width fonts such as the one used in the Sources panel. I read variable width fonts much easier than fixed. Also, some people like to read
their code with a range of colours like a bowl of fruit-loops. I think it is a bad idea and distracting. So it would be nice to have some control over that as well.
The ability to edit the style sheet associated with the Sources panel would be fantastic.