Say you have a widget toolkit that doesn't support touchpad gestures. The maintainers of that widget toolkit would be more willing to integrate this feature if there's support in both Xorg and Wayland compared to Wayland alone.

I think he is saying that if it is brought to X it will be easier to convince Wayland to follow suit.

We'll see if that's true, or if we will need another round of sponsorship to achieve the same thing with Wayland.