The other thing you are ignoring is how this compares to non-SPS conversion scenarios.
For example, let's take your PE of 12 row. According to you, Govt take would $254B from the 30.2B shares it would have. Let's compare it to a different scenario.
Legacy shares: 1,808,147,120
SPS: Written down to zero
Warrants: Full 79.9% exercised - 7,187,609,695 shares
JPS Converted: 951,000 additional shares (or SPO to raise money to redeem at par)
EPS: $2.91 (weighted avg of FNMA $2.67 & FMCC $3.35)
PE: 12
Govt Take: $251.4B ($147.7B FNMA + $103.7B FMCC)
The Treasury can essentially reap nearly the same value by COMPLETE write-down as they can with your version. Fewer shares all around (7.2B Treasury shares vs your proposed 30.2B), but higher intrinsic value per share. And... Far Simpler!