> It won't happen because Apple won't give you the option.
What won't happen, havoc in the ecosystem? How is Apple relevant?
> Swift 3.x has a large amount of syntax changes.
Yes?
> The compiler helps with the refactoring but it's still work.
That's not what I'm talking about. A bit of drudge work is fine, the issue of the Python transition is that you get usually hard to debug runtime failures down the line, possibly for a long, long time. With Swift, I assume the compiler just keeps complaining until you've converted everything more or less properly, you may have a few nits but you don't keep finding new breakages.
