1) The biggest leap so far was the transition from Generation 2 to 3. Someone keeps saying its the transition to 3D. This is maybe the 4th biggest transition. The biggest leap is easily Gen 2 to 3. Graphically it's a transition from 1D to 2D gaming. On the Atari 2600, I'm controlling dots and stick figures, while on the NES I'm actually controlling discernable 2D characters, each with a unique look. Music is now a standard, while on the 2600 very few games had music. Even more important is the fact that every major franchise on the NES started from scratch. There were definitely big franchises on the Atari 2600, but none of them really stayed big by the time the NES came around. Most importantly, NES games transitioned away from the short, score-based, gameplay of arcade games to gameplay where the object was to complete the game. Now console games were made specifically for the home. This gameplay transition lead to the death of the arcade.
The transition from Generation 2 to Generation 3 was so dramatic that many people consider it to be an entire reboot to gaming. Gaming returned but in a radically different form from what came before. The transition from 2D to 3D gaming is very small potatoes in comparison.
2) For Generation 9 to even be considered as the biggest leap, it needs to cause the demise of an entire platform. That is what Generation 3 gaming did to the arcade. Perhaps cloud streaming will come up with new types of gameplay that are so interesting that it will kill off consoles? Imagine a world where most people play MMO and Battle Royal type games on phone or PC via streaming and consoles just die out. Not saying that will happen, but that is the sort of thing that would need to happen for this to be the biggest leap ever (or at least in the running for biggest leap ever).
If we are just talking graphics...nah, only a small percentage of people will be impressed by the upgrade in graphics.