When the block reward get enough small, more and more miners will be shut down, since it does not give miners enough incentive to mine when majority of coins were mined.
Since early days of mining, many miners were incentivized to acquire a big enough pie of the total coin supply. But after mining reward cut by half several times, this incentive will not hold, so it is important to have decent fee income to keep the miners on board. I guess at 6.25 btc block reward the fee could be getting close to block reward
its not so much the amount of BTC the block reward has that is the incentive to mine as it is the $ value that BTC amount represents. so we'd need to see price double every 4 years to keep miners happy i guess. sounds resnable.
The dollar value is irrelevant. This is like buying Alaska several centuries ago, you get a big share of the total available land on the earth, but maybe that land is not used for a long time
Bitcoin is like land, you can not imagine what kind of value would grow out of it, the only thing for sure is that the supply is limited, so many miners are rushing to reserve their share before something big happens