would it be possible, for example, to access the standard decimal library of C# or Python via Javascript, thus not having to wait for the TC39 spec / implementation? [1]
This is in fact possible for C# and Python, but especially in the browser you would want to have a small binary size, and avoid bringing along the whole runtime of these managed languages if all you want is a small functionality subset.
A very viable solution would be creating a decimal package with either a native Rust crate (I think there are a few decimal implementations) or with one of the goto C libraries.
That would be much smaller and faster as well.
An article posted last week on HN [2] also seems to support this hypothesis, this time with some numbers. The AssemblyScript program had 6% the filesize of the Rust program.
So it seems like, if you want small wasm libraries, AssemblyScript may be your best shot.
[1] https://youtu.be/J5Rs9oG3FdI?t=2133
[2] https://news.ycombinator.com/item?id=33761756Although it has to be said that you can get Rust code to be really small if you know what you are doing and work towards it.
But I recommended Rust or C because there are reasonably mature decimal implementations. No idea if there is one for Assemblyscript.
Would you mind opening an issue in the WAI repository [1] so we can follow up there? Thanks!