I don't have to elaborate techniques. If a determined (and potentially mentally unstable) developer decides to leverage their full control over the OS to make it happen can. I don't have to elaborate on the techniques which might or might not exist yet. Stuxnet only targeted specific Iranian systems, a needle in a hay stack, was spread did not harm random devices across the globe, and stayed mostly undetected. And this was done without "developer access" to the software itself. Is it hard ? Yes. Is it likely (especially given the knowledge of how GOS works) ? Perhaps not. Is it impossible ? Definitely not.
When the lead dev of the OS you use daily threatens to "publicly expose you" as a user, I won't blame said user to stop using the software. And even less, to provide such data point regarding the behavior of that developer.