> How about making print() user-friendly with flushing after every call,
> and if you want explicitly want speed - use buffered
> sys.stdout.write/flush()?

This is exactly the -u option of Python 2: use it if you would like a completly unbuffered sys.stdout in a portable way.

In Python 3, it is only useful to flush at each line, even if the output is not a console, but a pipe (e.g. output redirected to a file). But nobody asked yet to have a fully unbuffered sys.stdout in Python 3.