A base module inside the house instead of using the wireless directly. The doorbell would talk to the base module over some type of encrypted connection using a separate wireless network or bluetooth, and the module in the house would be plugged into the network, either over ethernet or wireless. The connection between the base and the doorbell would be configured to only allow for the voice/video/doorbell functions and that's it.

do what every lock do for the last century: do not leave screws outside.

further, I'd have one module inside the door, a little wire just connecting a dumb button to the outside.

granted installation would require a single drill hole, but it wouldn't be a huge fail like this.

Wipe the memory when the back-plate is removed? It certainly isn't perfect but will make it harder.

Host its own wifi, with small preconfigured bridge device to plug into spare ethernet port of router?

Bluetooth to wifi bridge.