There are some that do power negotiation on the input side, and then power negotiation on the output side so you can have your cake and firewall it too.
Not necessarily, if you find an exploit that allows you to install malware without user interaction, Mactans famously did that for an older iOS version.
I'd still argue that making good use of such an exploit and rolling out the necessary, physical infrastructure does not have a great cost/reward ratio.
Sure. But the number of targets you could acquire there is miniscule compared to simpler delivery mechanisms, via a malicious app download, for example, and you have larger costs (hardware) and added risks, e. g. being captured on CCTV during installation.
That's why I said, the cost/reward ratio is really off.