Alex Joni has finished up his bbb_parport cape and has them available for sale!
This cape provides support for up to 6 axis, and has an optional ADC for analog inputs. There is a DB25 connector that should allow direct connection of an existing LPT based CNC machine to a BeagleBone. If you're more interested in cutting metal than printing with plastic, this is the cape for you!
Great work, Alex!