Yeah, I get the runtime can be big, but letting gc cross module boundaries seems really bad for sandboxing. I also kind of wonder why we'd want to use those languages in wasm other than their libraries and runtimes. If all you want is gc and performance why not use JavaScript or typescript? C# or go after a ~20% wasm penalty isn't going to be that much faster than js right? Or use something like nim that compiles to js and get libraries as well. The case for wasm always seemed to be absolute max performance in a safer package, which would send you towards languages that support manual memory management anyway.
One of the improvements that you get from the coming Wasm GC proposal is an object model that is inherently more space-efficient than JavaScript. While a lot of speculative optimizations can make JITed JS (of the right form) run fast with few checks, the object model inherently requires boxing or tagging and is not as memory-efficient as what Wasm GC structs give.
