As a long time FreeRTOS User, let me say I agree with Richard Barry. The RPi maybe a great little platform for what it does, but it loses a LOT of its luster if you dedicate it to a FreeRTOS app.
Some big issues are that it isn’t designed to connect a standard ‘debugger’ to it to debug an embedded program from a remote terminal, but instead is based on the typical techniques of debugging with the debugger running on the machine itself, which pretty much assumes you are running Linux, and if you are running Linux on the machine, you aren’t running under FreeRTOS.
Compared to a computer, it is small and cheap, but compare it to real embedded processor board it is big, expensive and power hungry. It might be a reasonable choice if you need the large memory resources of the Pi, but then you often want some of the other things that Linux will give you too.