And the 777X's new wing and control system will be even "more modern."
It will be maily a "copy and paste" of the 787 while keeping some cockpit commonality with the classic 777s, so it will most probably not be "more modern".
It's not size that gives a smooth ride per se. It's mass and wing loading.
Not entirely. It is also a matter of structural stiffness and resonance frequencies. Many single gusts result in a fading oscilation of the airframe, so you get an "echo" of each gust as the structural answer of the airframe.
Anybody who has flown in the forward end of the MD-11 can tell about the effect of a long fuselage with a heavy mass on one end...
As there is plenty of aerodynamic damping on the wing, mainly the fuselage stiffness drives this behaviour. Wing stiffness however determines how hard single gusts hit the cabin.
The A380 fuselage is short and high, it is enourmously stiff in vertical bending, hence almost no resonance (frequency is mucht to high).