I don't see any "hard barriers" but a lot of soft issues that will take time to overcome. As of now, there isn't even a uniform event handling framework in JS. So, first, we'd need a good generic 3d framework. Next, we'd need a significant speedup in performance across the major browsers. If OpenGL is a model, there would probably have to be some graphics-specific optimizations made, which might be difficult to get everyone on board for. Third, I'd either need to buy a new computer or JS would need gpu access, because ATM this site brought my relatively face computer to a grinding halt... and I don't think I'm going to have money for a new comp for at least a year or two :).