We already have banks, savings accounts and there is no reason why management fees would have to be any more than a normal savings account IMO.
Create a law that lets any bank savings account become a DTI Account (Don’t Touch It) that receives the 12% or so normally going to SS. Any other activity before the person is, say 50, becomes a taxable event (just a little incentive to leave it alone) except for major medical expenses.
Just an idea.
Sounds reasonable to me. (Seek, here's an idea from another FReeper.)