You are proposing a decentralized storage solution that is hosted by the witnesses of which the memory capacity is distributed to all Steemians in proportion to their SP holdings. I like this idea very much!
I understand that an economy can evolve from this where unused memory space is lent to those who require more of it. My first question though is, how are the witnesses reimbursed for this hosting service in the first place? I´m asking because the SP of the users doesn´t actually pay for anything unless it´s liquified and transferred.