Ah damn I thought this was going to be available to JavaScript. Would be amazing for one use case I have (an HTML page containing inline logs from a load of commands, many of which are substantially similar).
Maybe eventually (as a different spec). We've talked about wanting to support it in the DecompressionStream API or something similar at some point.
If you need it to be able to do compression though then it might be a harder sell since the browser doesn't ship with the compression code for zstd or brotli and would have to justify adding it.
There's wasm modules that do similar but having it bakes into the browser could allow for further optimization than what's possible with wasm. https://github.com/bokuweb/zstd-wasm
I have no idea if it's possible but I wonder if a webgpu port could be made? Alternatively, for your use case, maybe you could try applying something like Basis Universal; a fast compression system for textures, that it seems there are some webgpu loaders for... Maybe that could be bent to encoding/deciding text?
If you need it to be able to do compression though then it might be a harder sell since the browser doesn't ship with the compression code for zstd or brotli and would have to justify adding it.