I wonder if that would generate a financially significant amount of BTC. Would they ever actually mine a block with that little compute?

If nothing else, it'd generate a financially significant amount of USD for Apple :)

In a vacuum, yes. If you account for the fact that a large majority of people would get pissed with the battery drain and return their phones, no.

if the hash rate drops by a sufficient amount, then they could :)

So it's not the battery going