I agree with all of these. I think the biggest worry is that graphics cards manufacturers will be, justifiably, very reluctant to ramp up production due to the

I agree with all of these. I think the biggest worry is that graphics cards manufacturers will be, justifiably, very reluctant to ramp up production due to the how volatile the crypto currency ecosystem is. If they first ramped up production to meet increased demand, your scenario 1 (crypto market crashes) would hit them double hard since not only will they not be able to sell lots of cards to miners, but the miners will be selling their used cards for cut-rate prices.