The fact that there even is a separate SDK for it is rather annoying IMHO. If you want a sustainable ecosystem, you create one SDK. Then you write an open-source shim layer to adapt it to FreeRTOS mainline (where necessary) / add support for it to FreeRTOS mainline (where possible).
Presto, somebody else can do the same thing for any other RTOS.
Actually, now that I think of it, right now my best bet (assuming I want to spend that much effort, which is still up in the air) seems to be to replace the FreeRTOS-specific bits and pieces in the code I’m adapting with RIOT-specific bits and pieces. RIOT has an Arduino shim, so it’ll support the Arduino-ish parts without ripping those out also, and it runs on top of FreeRTOS (ESP32) as well as on bare metal (ESP8266). The problem is that platformio doesn’t support it (yet(?)); see RIOT-OS support · Issue #3456 · platformio/platformio-core · GitHub