Hacking bits and pieces from meshtastic's firmware is most probably the fastest way.
Meshtastic is currently using cheap esp32 which act as interface between end device and the LoRa radios. The meshtastic app uses the radio via the esp32's bluetooth or wifi. Serial over usb also works. Some people use card radios like the t1000 magsafe'd to their phones, which is cool. I am sure these things will become smaller and smaller in the coming years.
If the transport layer for bitchat becomes fully agnostic, this can be easily prototyped. Logically, making this work over LoRa, which has a very low bitrate and hourly frequency utilization limits, would pose some interesting challenges.
Let me know if you find this interesting, I'll gladly help hacking the firmware and testing it with the radios
