This is really a deeper issue than just a mortgage crisis. Buying residential property has been a fad so prices have spiraled way out of whack compared to most other sectors of the economy.
Way out of whack at least in many regions.
How many TVs would it take to buy one house in 1965 versus today? It's almost like a split has formed in the economy. Most prices stable, residential property and a few other things skyrocketing.
Sub prime defaults simply means a lot of the people who got sub prime mortgages can't afford this market. The creative financing is an attempt to make something seem affordable that really isn't.
Renting has it's merits, but it's not the fad.
There's just too many people trying to carve up too little land and the slices are too big, for the most part.
Smaller dwelling units and more compact communities would be a help. Also, of course, reduction in the growth rate of population. Maybe there's too many dollars floating around from years of low interest rates. Something has caused house values to go through the roof.
That's not really a banking problem, but it's a deeper philosophical issue that can be missed by folks using "compartmental thinking." It's easier to just define this as the "mortgage / banking / financial crisis." That's really just a symptom of the larger issue. The issue of carving out a sustainable place to live on this planet for the millions and millions of "more people" who are coming.