On the other hand, all the remaining bitcoin will be mined for over a hundred years. If we imagine that the price of it will grow exponentially, as Saylor expects, and traders will continue to trade bitcoin (existing coins will not 100% be pledged for loans, but also move on exchanges), loans taken in fiat will be covered by the rising price of bitcoin through the reduction of the collateral fund for such loans.
Sure. But the rate of BTC issuance is already the lowest rate of all commodities. So, most of those 100 years will be just the tail end of issuance. Fiat nominated debts are beside the issue. If you take a fiat loan today, you know it will be cheaper tomorrow. Interests on BTC nominated debts are not sustainable on the long terms. If you take BTC loan today, you know imagine (to use your own words) it will be exponentially more expensive to pay back. The only way to pay it back properly is to decouple btc from fiat, and then we go back to my argument; given issuance rate halves every ~4 years.