The consolidation in the RTOS space is starting:
https://os.mbed.com/blog/entry/Important-Update-on-Mbed/
This is likely a result of Zephyr, which is moving so fast that nothing else has a chance of keeping up as a general RTOS, especially for connected devices.
This illustrates the reality that even large and well-equipped companies (like ARM) cannot create and maintain some of the core technology we use today – multi-company open-source projects are the path forward.