Nobody has to upgrade. m68030 Macs still worked after the PowerPC transition. I used my Mac mini G4 for years after the Intel transition, and still use both an m68030 Mac and that G4 mini with NetBSD now.

Currently I'm running Sonoma on a 2010 MacBook Pro. I'd love an ARM-based Mac, but can't afford one yet. I'd have to disagree about the idea that "time is ticking"...