This is worth reforming, but almost no one except Americans also gets to get a 30-year fixed-rate mortgage. And this is a major boon for stability and predictability in American homeowners' finances.
Wait till that becomes a 40yr fixed rate. I see two viable ways to unlock the current supply/demand stalemate in the US (please chime in if you can think of other alternatives). People can't afford the 30yr payment (interest rates), can't drop interest rates (inflation), supply dried up because who is giving up that low rate for a higher one. So push the payments out over a longer period of time and drop the monthly…
This would probably increase the interest rate of new mortgages. Right now, lenders have data that these loans average around ~10 years, and thus have a premium over the 10 year treasury. If they get closed less often, because they can be carried around, we'll see the average as maybe ~15 years, which is a higher interest rate treasury (10-20) and will have higher interest rate costs.