so as a takeaway: expect volatility within the mortgage rates in the US ➖ upwards pressure: financial downturns in other sectors, organic de-leveraging ➖ downwards pressure: QE, Fed facilities, government policies
the US mortgage bubble will likely pop alongside other bubbles, due to a high degree of interdependence and correlation within the financial sector the mortgage bubble can both, trigger and be triggered by burst of other bubbles so you'll see a cross-border systemic downturn