I want DOM access from WASM, but I don't want WASM to have to rely on UTF-16 to do it (DOMString is a 16-bit encoding). We already have the js-string-builtins proposal which ties WASM a little closer to 16-bit string encodings and I'd rather not see any more moves in that direction. So I'd prefer to see an additional DOM interface of DOMString8 (8-bit encoding) before providing WASM access to DOM apis. But I suspect the interest in that development is low.
Tbh I would be surprised if converting between UTF-8 and JS strings is the performance bottleneck when calling into JS code snippets which manipulate the DOM.
In any case, I would probably define a system which doesn't simply map the DOM API (objects and properties) into a granular set of functions on the WASM side (e.g. granular setters and getters for each DOM object property).
Instead I'd move one level up and build a UI framework where the DOM is abstracted away (quite similar to all those JS frameworks), and where most of the actual DOM work happens in sufficiently "juicy" JS functions (e.g. not just one line of code to set a property).
