Is Coinbase "loaning" out the Bitcoin users have deposited in it?
The reason banks need the FDIC is that they loan your deposits out instead of throwing it in a vault and sitting on it, so if they go under they don't have those assets to distribute in a bankruptcy. Given how immature and non-economic cryptocurrency is, it wouldn't surprise me if Coinbase was sitting on all/most of its users desposits. So it's possible the users might get most of their deposits back after a bankruptcy proceeding (assuming the reason wasn't massive theft of assets or something).