Pennies and nickles would do the same I think. Probably work on any other acidic vegetable or fruit. And yes, a 9v battery or three or four positive to negative taped AAA or AAs would, I think, produce the same results. Coated lint or ordinary cotton balls for tinder.

I've seen copper wool potscrubbers, I wonder if they would work as well if not better by virtue of their lower heating temperature? or is the steel's key to heating its electrical resistance?

Good to see someone thinking outside the box.