To answer your question: Just as an example... Maybe a future (or present) feature can be used to activate the (built-in Wifi) network adapter of my device which I carefully disabled? Maybe it works as a trigger for other software or even OS components to start the network adapter? We will not know it until the day it actually happens. That's what they call vulnerabilities/exploits.
That's the problem and the point I am trying to make. You are not supposed to have network adapters and WIFI cards present in your airgapped system. They should be physically removed. If they aren't there, a bug, vulnerability, or malware can't activate something that doesn't exist. That's why I said properly airgapped device.I expect the threat coming from Electrum itself to be smaller than potential threats coming from other software on the average PC. If you want to remove features from Electrum to reduce potential attack vectors, you'll need to do the same to your entire operating system.
So keeping it offline is much easier
Since we're going in circles, I'm not going to reply again if it's about my security model.
There's a reason for that: Electrum security can't be seen on it's own. It's not a standalone device, it's a small part of much more software you're using.