> where does the 1ko barrier come from? Was it only chosen out of
> performance considerations [...]

Most certainly.  I’ll look at the history of the file later to try to find the developer who decided that.

> tempfile.NamedTemporaryFile was already used in python 3 (fixed in
> r57595, with not many explanations though).

That’s a TemporaryFile, without a name.  For more explanations, follow the parents of the changeset and you’ll find aee21e0c9a70 (referencing #1033) and cbd50ece3b61, where you can see an XXX note that is probably the “wish” referred to in the cryptic commit message.