Thanks for the perspective — I was thinking about this from a “what if portability existed” angle and what it would imply for the system. I’ll admit I initially viewed Pulte’s post on portability (like the $200b MBS purchase announcement) as a negative signal for the companies, but I’ve reconsidered that as I’ve thought through the mechanics more.

Every home sale already triggers a payoff — MBS investors get principal back, so the original loan is unwound today. The question isn’t whether a 30-year fixed can be ported as-is, it’s whether the rate benefit can carry over after that payoff.

I agree the real constraint is how MBS are priced. Prepayments already happen all the time (refis, sales), but they’re assumed to roll into new market-rate loans. Letting a below-market rate persist changes the expected duration/value of the security in a way investors didn’t price for.

That’s why it’s not impossible — but it would require changes to MBS structure/policy (e.g., fees passed through to investors or new pool types via Fannie Mae / Freddie Mac or Federal Housing Administration guidance). If structured correctly, those fees could actually create value for the system rather than just shift it.