To some extent (not capabilities), Haiku fits the bill here (https://en.wikipedia.org/wiki/Haiku_%28operating_system%29). Applications are bundles (but not WASM of course). The UI is very clean. The whole OS is also elegant and very fast on modern hardware.

Yes because BeOS was way ahead of its time. A complete new OS, doing all system things so much more efficiently, that it could allow wasting cpu time on high level actions, like moving windows in real-time while they were playing videos. On 1993s hardware, impossible with Windows or OS/2.