Bbanbob, I think you misunderstood me. I'm not saying the parent corp, WMI, or one of of its subs cannot participate in ownership of the MBS securities... but WMB, as the originating bank of the underlying loans cannot retain ownership in the securities. I've looked into this awhile back, and I believe securitisation rules prohibits the originating bank of the underlying loans from owning the securities. The originating bank (WMB) is only allowed servicing rights.
So any ownership of the securities must be under WMI or one of its subs. Not WMB. So if FDIC gifted these securities to JPM as part of WMB sale, they would be illegally gifting WMI assets.