New frontier? They've been popular for over 20 years.
I clearly remember in my machine learning class, one professor mentions neural networks and says it is slow and impossible to tame when the layers goes up thus loses its popularity. That is just 3-4 years ago.
Deep learning has really only recently become successful
hinton coined the term "deep learning" around 2006/2007 (more around deep belief nets/RBMs, but still, same thing), if that's considered "recently."
constrastive divergence and convolutional neural networks.
CD was also ~10 years ago. CNNs were reading your checks and postal zipcodes in the mid 90s.
successfully train the network.
In the early 90s, RNNs were driving cars on highways using only webcams under basically VFR. No giant sensors, no LIDAR, no GPS, no mesh networks, just camera input.
Before that there was little evidence that any form of neural network was massively better than other forms of machine learning. Now it has become clear that isn't the case.
Recent hardware made it possible to train more layers and they're now getting cutting-edge results in many areas again so they're now getting more attention again.
(Yes this is hyperbole, but any old timers out there will know the feeling)
Also "Past decades was AI winter. But no worries, now we'll start seeing human intelligence in a about next year" probably heard that since late 90's.