Yes, the idea is to write a coffee script in C4D.
But to be honest, so far, I've only used simple expressions in AE and simple Xpresso in C4D.
From AE to C4D by hand works quite well but it's not really fast : export data from AE, format it for C4D (this part involves a spreadsheet editor to invert Y axis), create a spline in C4D, import ASCII data to define the spline points, attach the camera's position, the camera's target or the layer's position to the spline, match C4D's amera with AE's.
So AE's script would only have to select relevant layers (based on layers name), copy relevant data, process and format it for C4D, create a txt file.
C4D's script would look into a folder containing relevant txt files, create each spline, camera, target,layer, light... with correctly set tag (attach to spline)
This doesn't seem impossible to do to me because I can understand needed steps, but maybe my lack of understanding of how both AE's scripts and C4D coffee work makes me believe it when in reality it isn't.
I know it's a long process, but hey, it's a good way to learn.
P.S. : someone on AE's list posted me this link http://www.creativemac.com/articles/viewarticle.jsp?id=42002
. It seems there already exists an Xpresso doing part of what I need.