>Would you have two string types - py2string that accepts anything and py3string that only works with utf8? Yes. A single naive one for py2 and two separate ones for py3 bytes and unicode. All casting between the two would have to be made explicit.

> How would this all work with C modules? In non-strict mode, you'd be able to use either py2 strings or py3 bytes with these, and gradually move all modules to strict mode which requires bytes.

And then, gradually after a decade or so attempt to get rid of all py2 types.