By logic of doubling prices , In next 40 years ,BTC should cost more than 7 million USD per BTC. I just wish if it can be true.
Historically speaking that's not entirely impossible. We've gone all the way from less than $1 cents to $8k-ish now, which is 8k times. I'm not surprised if it can do the same thing again but for sure we can't rely on such prediction. Mining needs to be profitable, so either the code changes or miners find another way to mine, like using green energy or highly efficient device.
I am guessing that sooner or later there will be more efficient mining device that will replace those in use right now. This is a must since many are also concerned on the power needed towards the bitcoin mining industry. With less cost yet bitcoin rising into the moon, mining can remain profitable for a long, long time until there is no more to be mined and that's when confirmation fees will be the only available source of revenue.