re. bubble, like the guy with the noble prize says, no one can even define a bubble. re. qe - everyone (2-3 years ago even more everyone) loves to blame qe, but there's no real evidence that qe has caused asset price inflation. it is becoming more clear that for the past 5 years, growth was low and there were global deflationary pressures which were more than adequate to explain the low interest rates. it is much harder to predict if the next 5, 10, and 25 years will see the same environment, but if most investors expect that it will, then asset prices are pretty rational.
if asset prices fall in the next four years, it will probably be because the consensus about the direction of growth/interest rates changes. will that have made the current situation a bubble? like the guy says, there's no way to say.