Motorola MG7700 / BCM3384 poking

Well, Comcast decided to stop supporting the router/cable modem I bought on their instruction, and have changed something recently which causes signal drops more or less mysteriously. I got a replacement from Motorola support, and the symptoms are identical still.

So, I have two of these things and figure I can spare at least one to poke around and maybe brick it.

Support for the device itself, and its chipset more broadly, seems to be pretty lacking.

I've found:
Some info on the chips/parts used.
A fairly rough overview of some of the Broadcom parts and their other uses (if this investigation bears any fruit I can try to throw a list of those in here to make this info searchable).
And, through that, a few repos with open sourced firmware for some other BCM33XX/BCM63XX devices: the Technicaolor, Arris, and Commscope variants.

Added to this is the fact that the firmware updates are not immediately accessible to the user: your provider is supposed to have some remote magic to push those.

Apparently this device uses the VxWorks bootloader; I had considered trying to boot into something like Ventoy, but with no IO the value of that seems limited. Right now, I'm downloading Nessus to see if there are undocumented telnet or other ports enabled on the device for connecting & poking around a bit further.

So, with the understanding that there's a good chance these devices won't ever be running OpenWRT: any suggestions?

(Also hi, I'm new to the forum. Let me know if I can do better on formatting or provide more relevant information going forward:)