This document describes the firmware release cycle.
https://documentation.meraki.com/Architectures_and_Best_Practices/Cisco_Meraki_Best_Practice_Design/...
What it doesn't mention is that a certain percentage of devices globally have to be running a specific release, with minimal issues, before it can be promoted to a "stable" release.
So if no one upgrades, it can never be declared a stable release.
Because the stable release canidate is being pushed out now, the chances are it will push over that threshold soon, and that same release will get declared "stable".