Currently for a parcoords.ParallelAxes() you can change the number format, fontsize and label rotation, but not the figure size (or aspect ratio). If you have many variables this can be desirable.

A maybe even broader approach to this issue would be returning a matplotlib.pyplot.figure instead of a NoneType when calling ParallelAxes.plot(), for which you can change it's size and other aspects afterwards (with Figure.set_size_inches()).