So it's been a while since I had my OS and microcomputer architecture classes, but it really looks like GoFetch could be a real turd in the punch bowl. It appears like it could be on par with the intel vulns of recent years.

which would have this hardware issue but don’t have actual background processing

So I've read the same about iOS only allowing one user-space app in the foreground at a time, but... that still leaves the entirety of kernal-space processes allowed to run at anytime they want. So it's not hard to imagine that a compromised app could be running in the foreground, all the the while running GoFetch trying to mine, while the OS might be shuffling crypto keys in the background on the same processor cluster.

The other thing I'd like to address, is you're assuming this code would necessarily require physical access to compromise a machine. That is certainly one vector, but I'd posit there's other simpler ways to do the same. The two that come to mind really quick, are (1) a compromised app via official channels like the app store, or even more scary, (2) malicious javascript hidden on compromised websites. The white paper indicates this code doesn't need root, it only needs to be executed on the same cluster where the crypto keys keep passing through by chance; so either of these vectors seem like very real possibilities to me.

Edit to add:

I seem to recall reading a paper on the tiktok apps with stock installation were actually polyglot, in that the app would actually download a binary after installation, such that what's executed on an end user's machine is not what went through the app store scanners. I had read of the same for other apps using a similar technique for mini-upgrades, which is a useful way to not have to go through app store approval everytime you need to roll out a hotfix or that latest minor feature.

If these mechanisms haven't already been smacked down by apple/google, or worse, aren't detectable by apple/google, this could be a seriously valuable tool for state level actors able to pull off the feat of hiding it in plain sight. I wonder if this might be part of what congress was briefed about recently, and why it was a near unanimous vote to wipe out tiktok. "Hey congress people, all your iphones are about to be compromised... your tinder/grindr/onlyfans kinks are about to become blackmail fodder."