Given that all the external factors are pretty good right now (interest rates, jobs [for now], etc.), I don’t see anything that can reverse the trend. Absurdly low interest rates might help, but even then, it would just be the final last gasp (and I don’t really see that happening anyway).
40 year mortgages certainly aren’t going to do it as these are still more expensive on a monthly basis when compared to the interest-only loans that have been so popular in the last few year. Also, as loan term increases, they effectively become interest-only loans anyway.