The obvious question is "why bother". I can see that this software emulation of a USB 1.1 stack might be useful for Arduino boards, because as the V-USB page says it makes "it possible to build USB hardware with almost any AVR® microcontroller, not requiring any additional chip". Arduino boards (except Leopnardo, and those boards with a second, USB host port) don't have a USB 1.1 stack. Instead they have a serial (UART) to USB converter.
All the Teensies have a full, hardware, USB 1.1 stack separate from their serial UART or UARTs. So this would only be of use if someone needed two, separate, USB connections and couldn't or didn't want to make a single, combined type.
Did you have a particular application in mind?