The new novatek SOC seem potent enough, but of course if you then ask it to pull several cameras then you dont have much left.
Actually the new Amba stuff also look very capable
I am still wishing for that MEGA / Race dashcam, that operate in action camera territory and with a blistering image quality, but of course for that and not least in a car cabin environment i have doubts about a SD card having the guts to cope with that.
I would buy such a dashcam even if it was just single channel or maybe dual but then the rear camera was its own unit, and was only powered and timed / synced from the front unit as it would otherwise be a system on its own.
I would still be OK with a rear camera having its own memory card, CUZ i know it is not often i will have to go to it for footage, but it would also be nice to have it as part of a total package with a smart footage recovery system so i still wouldn't have to handle its memory card as events from that would still be tied together with the front system.
Also some phone image processors also able to handle a lot, insane pixel counts sensors and multiple of them at the same time.
My imagination is as vivid as ever.