Dubz Brilliant! Let me just go buy a tablet and carry it around in my pocket. That won't be obnoxious or uncomfortable or anything... /s
It's not bad advice. If your threat model requires to never, under no circumstances, turn on the cellular modem (which your request somewhat implies), a Pixel Tablet can be a great deal for people willing to carry it in the backpack. Not having a cellular modem in the first place is the best way to not use it by accident.
Dubz apps occasionally popping up asking to re-enable camera/mic access (which is annoying that it can't be disabled in itself)
You probably mean the global camera/mic toggle. The popup only comes if you give an app the camera or mic permission, in which case it can be assumed you want this app to use the camera or mic. If you remove the permission for the app, this won't happen again (a badly programmed app could annoy you with
in app pop-ups asking for permission even when not needed, but that's on the app developer and nothing GOS can change).
Overall I see the benefits of PIN-locking airplane mode, but I assume it's not a high priority feature compared to something like location scopes. Definitely worth to open a request on Github if you want to draw the dev's attention to it.