Here are some different things that seem potentially valuable which we could consider to produce next year, roughly ordered by how useful I think they would be, with the most useful at the top. It's possible I forgot some things.
Right now, I observe that not many people are making any XR thing on the web. Part of it might be that WebXR is new, but part is that it's relatively bad. Naively, my guess is that three.js and A-Frame tooling and performance (and WebXR browser features) is where most of the gap is, and making them more competitive with Unreal or Unity would be attacking that problem. Something like the Unity editor, for example, would go a long way. Improving networked-aframe could be useful. Adding browser features to make the experience of using WebXR smoother could be useful. I defer to