Corker has already signed up to be the broker. He will sell them at a silent auction during the State of the Union speech. He has supposedly agreed to do it for a measly 20 percent cut.
Do you think TSY would sell on the open market or in an offering?
I do not know what Treasury will do with the GSE issued senior preferred stock. The GSEs are not the only ones to issue senior preferred stock and warrants to Treasury. Through Treasury's Capital Purchase Program (CPP), Treasury received senior preferred stock and warrants worth billions of dollars for troubled banks and financial institutions. The Treasury allowed CPP companies to redeem or repurchase senior preferred stock or Treasury sold the same. See this latest Monthly Report to Congress on TARP for details - https://www.treasury.gov/initiatives/financial-stability/reports/Documents/2015.11%20November%20Monthly%20Report%20to%20Congress.pdf
There are precedents and several options (redemption, repurchase, auction, sale, transfer, etc.) open to Treasury. Which one will it be for now is wait and see.