I doubt that it's feasible to reimplement GUI widgets. They require tons of micro behaviors. Revery will need to implement not just the looks, but also input, with a bunch of different devices in various configurations―which means lots of possible combinations and interactions between the elements.

Since Revery doesn't use native widgets, it will lose all advanced native features―e.g. nuances of input handling, and automation―or will have to reimplement them one by one on the low level, polluting the code with native paradigms from each platform.

Browsers and GUI toolkits spent decades on this, and still they lag behind, as evidenced by QT's non-support of keyboard remapping on MacOS (i.e. sane “home” and “end”).