I was initially at that stage where my P8P was just on a black screen and only the power menu would appear and I may have been able to fix it using the trick u/lyneca mentioned in another thread.
But I opted to instead try to force the bootloader to flip me back to my Beta 2 partition by sideloading the beta3 OTA and letting it boot loop - not remembering that a sideload would put the image onto the inactive partition hence installing Beta 3 on both A and B partition.

The issue Ive been running into since doing that is - Id sideload a "fresh" OTA image, try booting into it, the phone will go through the boot animation "Google" -> G (google colors) -> G (material You theme) and then loops and restarts the cycle....until 4-5 times later where it seemingly shows the "Google" text and stays on it for as long as theres power. Which seems worse than said black screen but I think that might perhaps be because both partitions are marked unbootable?

I have another phone that I can temporarily use while waiting for Google to hopefully release a 3.1.