The Web of Things direct integration pattern [1] (running a web server directly on a device) is not a good fit for MCUs, with a few very high end exceptions (e.g. ESP8266 and ESP32 for which the WebThings Framework works perfectly well).
For constrained devices like MCUs the gateway integration pattern is a better fit, which means using some other low power communications mechanism on the device itself and having a gateway bridge the device to the Internet and the Web of Things.
It's also within the charter of the Web Thing Protocol Community Group to explore a more lightweight CoAP+CBOR alternative to the default HTTP+JSON sub-protocol, which may help in some cases.
