Earlier quoted context omitted.
I suspected that someone would mention this, but the fact of the matter is both systems are mostly interoperable. The switch from npm to yarn would be nothing like migrating from Gulp + Browserify to Webpack. To switch to yarn, I printed out a one-page cheat sheet and taped it to my wall. I’ve had one blunder in the time I’ve used it (misunderstanding what `yarn upgrade` did x_x), but it was easily reverted.
I think you're making TeMPOraL's point, though. Even in this relatively close case, it's not a zero-overhead transition. There are some changes. There are some new behaviours. You still need to know which things really work exactly the same and where the differences come from even if those differences are only minor. You always need due diligence about whether a new tool is reliable, future-proof, trustworthy, etc. A…
It’s also laughable that npm is accused of being a hack and yarn is accused of being over-engineered.