Have you monitored the MQTT messages exchanged? It is extensively supported by MQTT which is something HA and openHAB support for sure. Both monitoring and control messages are supported.
Please also keep in mind the HestiaPi Zero which will probably be available within 2021 and suits better your needs. We hope within the next month, once production for HestiaPi ONE with the new Chinese factory is starting to run smoothly, to focus on Zero and release some more solid info, specs and photos.