When all the 21 million Bitcoins are mined and put into the circulation, prices would proportionally go up and with relationship to the adaption too.
As of now, we know that some countries are still not accepting bitcoins, yet we do not know if  there are people already who holds some cryptos with them. If we would think that they do not have any. There will be a great chance that 50k USD is not the highest price per bitcoin. Everything will be so expensive when every coin is being distributed.