Putting a Regression Line When Using Pandas scatter_matrix
I think this is a misleading question/thought process. 
If you think of data in strictly 2 dimension then a regression line on a scatter plot makes sense. But let's say you have 5 dimensions of data you are plotting in your scatter matrix. In this case the regression for each pair of dimensions is not an accurate representation of the global regression.
I would be wary presenting that to anyone as I can easily see where it could create confusion.  
That being said if you don't care about a regression across all of your dimensions then you could write your own function to do this. A quick walk through of steps may be:
1. Identify number of dimensions N
2. Create figure
3. Double for loop on N, first will walk down rows, second will walk across rows
4. At each point add subplot, calculate regression (if not kde/hist position), plot scatter cloud and regression line or kde/hist
I'm using scatter_matrix for correlation visualization and calculating correlation values using corr().  Is it possible to have the scatter_matrix visualization draw the regression line in the scatter plots?