OpenAMP focuses on RTOS running on "subordinate" coprocessors.

This is more of a good old classic partitioning, which was rare outside of hardware with special support for it.

Most RTOS + non-RTOS combinations use RTOS doubling as hypervisor, with RT tasks running at guaranteed timeframes and non-RTOS guest running in more relaxed form.

You can also use it in a "SMP" processor. For example I use it on Zynqs which are dual or quad ARMs symmetrical ARM SoCs. Linux or the bare code can be the master or subordinate.