It's a hard question to answer. Not all systems are equal in size, scope, and impact. K8s as a system is often the core of your infra, meaning everything running will be impacted. That coupled with their team constraints in the article make it sound like a year isn't awful.

One system I can think of off the top of my head is when Amazon moved away from Oracle to fully Amazon/OSS RDBMSs a while ago, but that was multi year I think. If they could have done it in less than a year, they'd definitely be bragging.