Re: Solving the cube not so important
If it takes the equivilent of 10,000 years to 'train' this robot to a 20% success then it's slow machine learning not AI. Having said that, if it can be improved to the point where retasking to any other 'one-hand problem' reaches a similar level success within a few weeks then we're well on the way to a general purpose robot that will render the need for human manual interaction with any environment optional.
As the only useful purpose of a robot hand is to manipulate the items we've designed to be used by hands (quite literally, everything) I see these robots main use in and around the home, "Robot, Make me a cup of tea, butter some scones then mow the lawn and prune the roses" or more likely "Help me out of bed, help me in/out of my stairlift, give me my medication..."
Everything outside the home environment will be better served by custom built designs as is happening now.