You can run RTOS on M0+. You have to manually include the RTOS files and configure them since PSoC Creator FreeRToS support is limited to the M4 core.
You can't run proper linux / Android on M4, or any Cortex M / R series CPUs for that matter, because they lack memory management unit (MMU). That being said, there are forks of linux kernal such as μClinux, which can run on CPUs without an MMU. However, even these forks have very high memory requirements that increase the BOM cost significantly.