possible to preform VIO from two cameras/imu's on a dual-core esp32?
I haven't worked with the ESP-32, but it seems to me you're quibbling over pennies. Pis are cheap and very powerful. They run Linux, so there are tons of open source libraries available for them. You could install OpenCV, for example, and do computer vision quite readily.

I'd recommend at least a PI 3.

If you used an ESP-32 based system, would you run it as an Android device? Android's "OS" (And that the term OS is quite a stretch) is really just a setup function and a run loop. You should use a device with a real OS, including a file system, etc.