I am not super familiar with WebOS, although I did limited Palm development at one point. I believe it depends greatly on what code is included in the Raspberry Pi port.
R-Pi 3 has Cortex A53 (as does Gemini, as well as A72), but a Broadcom GPU.
At least one variant of WebOS does support a GPU from the Mali line, however, according to
http://webossignage.developer.lge.com/disc.../hardware-spec/I am not an OS developer or hardware engineer, so I don't know how similar the Mali T-800 series (in Gemini) is to the ARM MaliT-700 series that the WebOS 'signage' variant supports. But as far as CPU and GPU support, it seems like it could be worse. I know PalmOS used to support (infrared) keyboards and screen rotation, which would also be important to Gemini, of course.
I too would be curious if anyone else has more info