That certainly explains why the standardization process went nowhere. Ie. It was a UI feature largely specific to a single platform's native UI paradigm, and at that a platform with a minor marketshare.

Regardless, this is a great example of how innovation should happen. That is browser vendors try out new things, and those experiments that succeed become standardized. In this case it sounds like this experiment is a step forward, but not quite reusable enough to support standardization across platforms.