It's pretty simple actually. Either Jr. Preferred dividends get restored (which seems unlikely considering the interest rate environment). OR JPS get Converted to Commons at some percentage of Par Value ($25 or $50) at the time of the re-IPO -- which is likely going to occur around $5.00 [Pending Reverse Split].
It's not like the companies are going to Sell new FNMA Common shares just to "Call" the Jr. Preferreds at Par. Or in other words, ~$30B in additional dilution to Commons. That makes no sense and it's a heavier lift for the Financial Advisors who are already going to be raising the most capital in the history of IPOs.
Morgan Stanley & JP Morgan are likely telling the FHFA/Treasury/GSEs that their Options are limited.