Ouch. My quick mental math was quite meandering there. I'd put the not accounted for $100 into cost of doing business though, not the BOM. You have to pay for customer service, warranties, replacement inventory, etc. So 200 for BOM, 200 for profit, and 200 for cost of doing business. There'd be 0 to $50 of variance in the 3 figures quarter to quarter, year to year.
Every time I do that, the inevitable conclusion is to wonder why Apple would even try. They have to double their current unit sales numbers to really make a dent. There would be inevitable cannibalization, so it's quite the tricky proposition. And a $300 wrist computer? They'd have to sell 20s to 30s of millions per quarter just like the low cost iPhone to really make a dent as well. They are all side shows to iPhone and iPad revenue and profits. Apple has grown so huge that the "next big thing" for them has to be so huge that it'll encompass the entire population of the Earth. I'm not even sure being in the energy or public-sized utility business can make a big dent.
CO2 scrubbing robots?
Water collecting windmills?
Consumer power plants and energy storage?
Space power and weather control?
Buying out Bloom Energy, buying/developing CO2 capture techniques, water extraction are about the only billion, trillion dollar level blue sky businesses I can think of that allow Apple to be a 0.5 to 1 trillion per company a decade down the road.
Otherwise, they are going to meander along with an up and down business, fluctuating between 80b to 160b per year as a company. That might just be perfectly fine. Becoming more than that seems exceedingly hard to me.