Also, when's the last time anyone's installed a virus on Macs? They're infinitely more open than their mobile counterparts, yet there's barely any issues there.
I'm willing to bet the large majority of people don't even know what sideloading is in the first place, and even if you somehow accidentally happen upon an APK you need to go through some scary warning screens before it even lets you do it. I genuinely don't see this ever being an issue, it just sounds like shilling for Apple to keep their dominance and closed APIs