FWIW my home computer emulators [1] already run at about the same performance (give or take 5..10% depending on CPU type) in WASM versus their natively compiled counterparts.
Performance is already as good as it gets for "raw" WASM, the proposed component model integration will only help when trying to use the DOM API from WASM. But I think there must be less complex solutions to accelerate this specific use case.