I simply don't see the need for a new theory. If you have a monetary contraction its gone cause a huge problem with wages and prices and that has been the most solid empirical result in economic history. It explains tons of stuff that simply could not be explained by this high debt theory.
So lets just look at some basic evidence for that.
As you can see here:
https://marketmonetarist.files.wordpress.com/2014/09/ngdp-ez...
Is is totally clear that in order to go back to the original trend inflation would have to be above 2% for a short time to get back to the level. However the Fed and the ECB were simply not willing to do that. The Fed often repeated that they would do 'everything' but then followed it up with 'but if inflation goes up we stop'
However that policy does not make any sense. The monetary disruption has already happened and then they are massively below trend and are unwilling to go back to the original trend.
This policy however is totally mistaken because it makes macro economic sense to go back to the trend as you want to stabilize long term wages and prices and not force the whole economy to adjust to a new level.
(Btw this is called 'level targeting' and has huge support from many monetary economist)
Now, some New Keynesian agree that this should be the policy, they like the term 'flexible inflation tarting' because they assume perfectly rational central bankers that will figure out the right number but essentially the agree that 'the right number' is going back to trend.
However some of them believe this is not possible because of the 'liquidity trap'. However here is where this recession actually showed that their assumption is simply false. Many countries, like Switzerland have shown that if the central bank is willing boosting NGDP with zero interest rate is no problem. This was actually tough in mainstream monetary macro books before the crisis but somehow this was ignored because 'fiscal stimulus' was the politically favored narrative.
Lets look at one economy that didn't have a recession. Australia is a good example, they never had a drop in NGDP and they didn't have a recession even when their housing 'bubble' and many other things are not that different from many other countries that had a recession.
One more thing:
> other measures are needed. These could include quantitative easing, forward guidance ...
Well, if funny how nobody remembers history. Before the New-Keynesian revolution some of those tools were called 'monetary policy'. This nothing new, but rather the way monetary policy has been practiced for a long time. Central banks that didn't build their entire operational model New Keynesian interest rate theory were perfectly able to act at the Zero Bound.
By the way this is in many way the same problem as in the early 1930s, the theory for this is nothing new. R. G. Hawtrey spend the whole 20s to try to explain people what would happen if there was a nominal contraction and he was exactly 100% on point.