Linux can boot in under 10 seconds if you invest thousands of dollars in optimization but near zero boot time is simply a dream.  Typical boot times without extensive optimization are in the range of 30 seconds on most MCU and lower end MPU processors.  Zero boot time is simply not possible using Linux.

Unison can boot in microseconds.  The reason for this is the modular architecture that eliminates expensive and slow procedures at startup.  After an initial start of microseconds, Unison then initializes the servers in the system which do I/O.  This can take some time but to the user it is instantaneous.  From the user's perspective, Unison offers Zero Boot Time.

If the users of your system don't want to wait, and you would like to reduce your BOM costs, consider replacing Linux with Unison and reaping the benefits of Zero Boot Time, smaller memory and resource requirements, and a compatible programming environment.