This feels like bringing the annoying transitions people used to use between slides in PowerPoint to the web. There's nothing smooth about the transition in the linked demo, it's quite jarring.
I believe it’s finally enabled by default in nightly builds, so it should be standard soon. I may be wrong and it may have been scoped css enabled, but both are available by feature flags on nightly and plan to be enabled by default by the end of the year.
This just means that user doesn't get the animation tho, right? The actual page transition still happens, so you get graceful fallback without the need to do anything special.