The piece I quoted indicates to me that the parent possibly does not understand this about JavaScript since they stated the compilation cost of JavaScript "is zero" that implies that JavaScript is not compiled. If there is a compilation step then some cost is incurred no matter how low.
It was further supported that the parent may not understand JavaScript is typically compiled when they followed on with "cost being completely amortized with everything happening directly at runtime". That would indicate that all of the cost is incurred/paid at runtime rather than in the compile step which is simply false.
Also, that the parent bothered specifying "AOT" in the first place is proof enough the entire basis of your belief in their understanding of things is utterly groundless. This would be clearer to you if you understood that JIT compilation cost is amortized, as the parent alludes, and that it doesn't happen in "a" compilation step.
The tooling hasn't been the problem. There are compatibility libraries (ie: six), source transformation tools (ie: 2to3), and plenty of books, blog posts, and talks on how to manage supporting both version of Python or doing a full port.
If you want to port there's a well-tested and clear path. There are enough big libraries out there that have managed it. There is no real barrier as the OP suggested in their article.
Also, porting is made more difficult by the fact that Python is a dynamic language, so a lot of errors that could be caught at compile time will only be catchable through a thorough testing suite. I have seen little evidence to suggest that porting from Python 2 to 3 is actually straightfoward in the sense of not requiring significant effort proportional to the size of the code base.
ECMAScript 6 is finalized and many people are running it today in production environments either using Node on the backend or on the front-end using a build process that integrates with something like Babel.
The following quote implies that you believe JavaScript is runtime evaluated, when in fact the standards body does not specify runtime evaluation or compilation. That is a decision left up to the implementation. All major browsers today and Node.js use just in time compilation for JavaScript rather than runtime evaluation.
"The compilation cost for a dynamic language like Javascript is zero, the cost being completely amortized with everything happening directly at runtime."
[EDIT]
I have added a link to the JavaScript entry on Wikipedia where you can verify that modern browsers compile rather than interprest JavaScript.
https://en.wikipedia.org/wiki/JavaScript