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1. Bitcoins price increases dramatically and covers the ever increasing electricity demands
2. We reach an efficiency bottleneck with ASICs and electricity consumption requirements level off (seems unlikely and also you could just manufacture more asics - so I think this ones out)
3. Average fee price increases to meet the increased demand of electricity
4. # of txs increases to increase the total fees paid
5. Bitcoin doesn't increase in value, fees and txs don't increase, miners hit a bottleneck due to the cost of electricity and profitability. Bitcoin becomes less secure.
I think there are various other possibilities:
6. Huge technological advancements in energy extraction, which causes energy prices to plummet
7. Another cryptocurrency comes up with a better consensus algorithm than PoS or PoW and it gets adopted by the Bitcoin developers (unlikely, probably decades away if it ever happens at all)
8. A PoW change that makes Bitcoin mining less energy consuming
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However, I think #1 and #3 are the most likely outcomes. Coincidentally, these are also the developments that Satoshi set up in the
initial Bitcoin design. We can already see the price increase in the last years and the development of a competitive fee market (with all
the secondary effects like Bitcoin forks that are mainly caused by the fee increase on the mainchain).