Besides the big download size, it does several things very "right": Full Python data model, access to the full javascript model (albeit slowly currently).
Also PyPy is the right choice as the basis for this (as opposed to CPython) because its ecosystem is generally more "pure" Python than CPython's. C Extensions would only get in the way.
it's systematically translating the PyPy interpreter to the Javascript, so it has to get semantics right. However I'm not sure if the drawbacks can be addressed in the current JS model, notably: very slow warmup, huge download size (that's primarily PyPy fault though), the lack of good JS access.
> However I'm not sure if the drawbacks can be addressed in the current JS model, notably: very slow warmup, huge download size
Only for the first time loading it.
It would be great if some big organization (looks at Google) hosts the "standard" version of the file, much like jquery, so that it would be cached and ready to be used on the local machine most of the time.
Also PyPy is the right choice as the basis for this (as opposed to CPython) because its ecosystem is generally more "pure" Python than CPython's. C Extensions would only get in the way.