That's not really enough as you depend on libraries you don't own. All the sudden in order to update a small library you use you need to update to a new version

That's not really enough as you depend on libraries you don't own. All the sudden in order to update a small library you use you need to update to a new version of Python. So, yeah, new syntax is always disruptive. My utopia has new syntax being added very seldomly with loads of notice period and a `from __future__ import newsyntax` phase before the syntax is considered "production ready". So, hopefully, by the time people start using it, all relevant version of Python supports it.