Honest question: How often do people upgrade their production language? Me: once in a decade, maybe. I'm still perfectly happy (and productive) with C# 3.5, Java 7 and Python 2. I'm grudgingly moving forward because the old toolchains are being deprecated now, but my codes aren't significantly improved because of a few fancy idioms available in a new language, and it barely affects the design decisions. Upgrading you…
And if you have a reasonable testing environment, it's not rocket surgery to figure out how much of a problem a new version might be.