To be perfectly honest, it is not a big deal to implement a simple algorithm that would smooth your mouse made lines. It will, however, not be a satisfactory result no matter what we do. Drawing with a mouse is just not a good idea, unless you are just testing stuff or doing an extremely rough stick figure type animation. Our aim is to enable people to create high quality animation – so for serious use you just have to have proper drawing hardware. I highly recommend it.
We have plenty of important things still to do with Animation Paper, like the whole area of coloring, so I am afraid we will not be prioritising mouse smoothing. I hope you understand.
To maybe solve your problem, you should check out external smoothing softwares, that works as an extension of many drawing programs, including Animation Paper. Maybe others can suggest a good one?