One part of the OS that currently, but didn't, reply and dynamic memory was process and thread management. Previously, this was statically defined but with 255 processes and 255 tasks this resulted in around thread 65,000 entries. Each entry containing all the registers from context switches and some state. When linked it was around 14MB of data in the BSS section.
That's fine if you're running on a 1GB machine, much quicker and simpler than dynamic memory but if you're running on a 4MB ARM7 processor - less helpful.
This probably means that the thread and process management will have to follow suit behind the memory management. That is be broken into two models depending in the Memory Management model being used.
Typically with Embedded systems Threads and Processes are, once created, rarely created or destroyed to ensure (well it's good practice anyway). This means that dynamic memory deallocation isn't necessarily required as the chance of it being deallocated it slim and will yield small results anyway.
Therefore there will probably be two Process Management models that will be directly linked and derived from the Memory Management model.
1/ Dynamic Allocation & Dynamic De-allocation = Heap based Process Management
2/ No dynamic memory = Statically defined maximum number of processes and tasks.
To tune the memory the maximum number of threads and processes could be defined by the BSP so it was tailed to the memory requirements of the board.