I still wonder what would have happened if Java decided to take Javascript's approach by giving access to the DOM, rather than an entirely separate GUI mode.

Things like Google Maps and Gmail came as something of a shock. They were near-desktop-level apps entirely within the browser. That meant JS, not because of the language but because it was the only cross-platform system that gave access. It should have been possible to do that for Java as well, but they never really tried.