A lot of people would buy Motor just for this feature. Everyone can export shapes, but no one can import shapes from different packages.
Many companies I work for have artists using different packages because people use what they know, especially on short term jobs. A big roto job will have multiple artists working on a single shot. It would be great if we could combine all our roto together in Motor. Especially when you have an artist who forgot to turn on motion blur or they did the roto in the compositor which only supports exporting to their native file format(Shake, DF, Combustion, etc…), but the final comp is being done on an entirely different package(Flame, nuke, etc…).