Is there anything that suggest GoFetch/DMP attacks have been used in the wild? I haven't seen it mentioned on the usual sources.
Saying that, with the increase of malware on MacOS there's certainly the possibility of it happening but if you were infected with malware then you're fubared any way.
What will be interesting to see is if Apple will try and mitigate this with software fixes a la Spectre or, given software fixes are likely to affect performance, hold off, give the finger to existing users (especially M1/M2) and implement architecture changes (mostly like in the M4).
Edit - Just to add, M3 (and Intel) users are less susceptible to the attack as DIT (data independent timing) can be disabled. But realistically it's negligible this attack would happen to the average Joe especially if they keep away from the usual naughtiness of the interwebs and run malware scanners etc.