[llpg]

This.

Per Hyrum's law, someone will rely on any given behavior. So, if you choose backwards compatibility, it becomes harder for the committee to evolve the language over time.

The path of breaking changes can be made less painful, and does not, necessarily, invalidate all the code that is already written.

With that being said, the problem right now is not the decision of keeping backwards compatibility or not, but the fact that the standard should be explicit about it, so people know what to expect.