As you mentioned: the only thing that restrains moving to C++14 is the compiler support.
As far as I know there were some efforts building ROS2 on arm microcontrollers. Perhaps it would be wise to check if the most common compilers for embedded platforms are supporting C++14.
The arm-gcc-none-eabi compiler that is often used for STM32Fxxx series supports C++14. ( https://cppembedded.wordpress.com/tag/c14/ )