Hello
I've successfully "upgraded" my Anytone AT-D868UV to support the AT-D878UV Firmware. This is only possible on certain versions and involves dismantling the radio and flashing the STM32 MCU. I didn't experience any major hurdles and it went pretty smoothly.
More details are on
F5UII's Blog here. The only major difference is the 878 firmwares adds Analogue APRS and crude roaming. If you don't require these features, its probably not worth upgrading.
I have the required 3D printed tools for removing the nuts around the knobs and antenna connector, the ST-Link programmer and a "loom" for flashing the radio. If anyone wants to borrow them let me know.
Cheers