Proposal: Embedded Programming and Design
Does embedded programming and design include the use and programming of a real time operating system, or is that too high level?
Deciding if a RTOS question would fit into Embedded Programming and Design depends on the specific question. If it's a question about programming an good heap management it could also be a good question for Stackoverflow, but I would not decline it. As @Andrew said, a question about porting e.g. FreeRTOS to the needs of a specific controller would totally fit in Embedded Programming and Design.
Or another fitting question could be How can I get FreeRTOS to use my external RAM over [bus] for heap? This a little bit more than normal porting, and would not fit to SO or other sites.
In my opinion RTOS questions should be accepted, except it's a general programming problem (in the context of a RTOS), which can occur also in normal applications -> Stackoverflow.
Analog this should apply to questions about realtime kernel modules.