Based on what I have observed, T-20 is the new norm associated with Cricket and I don't have any qualms about it since I love how entertaining this format is and is my favorite one in my opinion.
I agree. Day and Night test matches doesn't represent the solution to curtail the falling interest in test cricket. There was a reason why a great deal of interest was there for the recently concluded Ashes series. And the same reason can be attributed for the (relative) lack of interest for the India vs South Africa series, which also concluded at almost the same time.
What attracts the crowd is traditional rivalry. Ashes is more than a century old, and a lot of people are crazy about the England vs Australia rivalry in cricket. In the past, there were so many controversies (such as the Bodyline scandal) and this rich history keeps people interested. India vs Pakistan rivalry is also comparable, but the two teams haven't faced each other in more than a decade.