Possible, although it would be rather difficult to do well in a flexible manner, and would be unusable by every app that currently exists. More or less, it woul

Possible, although it would be rather difficult to do well in a flexible manner, and would be unusable by every app that currently exists. More or less, it would be a replacement of the entire X event handling model, entire X drawing model, etc. And it would make writing apps more difficult -- very few of them use entirely stock widgets, and it would be nearly impossible to securely and performantly implement new widgets on this system. Plus, it's diametrically opposed to the X "Mechanism, not policy" mantra. I wouldn't expect anything like this to take off, but it's been tried in the Y window system, and more interestingly -- and more dead-in-the-water -- in the NEWS window system.