Cryptocurrencies have been designed as almost the perfect collateral. I joking call this possible future the "Cryptocurrency Pawn" model. Banks may eventually realize that bitcoin is the best collateral identified to date. here is a simple example:
Joe wants to buy a new car. He has bitcoin, but of course, he does not want to give up his $50,000 bitcoins expecting them to be worth $100,000 next year. Spending deflationary currency comes with it's own expensive repercussions, as anyone who as ever spent cryptocurrencies can attest. So Joe pawns (gets a loan on) some bitcoins. The bitcoins are locked into a smart contract. The bank advances Joe $50,000 on two $50,000 bitcoins. Joe pays back $1000 a month worth of stablecoins, and when he pays back the $50,000 his bitcoins come back to him, probably worth $250,000 by then. If he fails to make a payment, the bank gets his coins. There is a great incentive for Joe to pay, and essentially no risk to the bank. The bank can charge some nominal interest for an easy profit that in the end costs them essentially nothing.
Those collateral loans are highly overrated when it comes to a large purchase, most people who seek a loan from a bank don't have that amount in collateral in the first place, if they would do so they could take a mortgage. Collateralized loans in cryptos are done mainly between altcoins and BTC because you think the value will grow in a short period but this will also come to an end. You envision
BTC doing an x5 in 5 years, will it do again a x5 in the next 5 years? And so and on all this century?
Second, there is the risk factor, bitcoin dropped to 4k last April, if you would have taken a loan at 10k your collateral would have been sold to pay up your debt.
Look at your scenario from a different point of view, you take 50k, you deposit 2 BTC, the price drops by 50% overnight, your collateral is liquidated and after 1 month the price of
BTC goes back to 50k. If you would have sold one BTC you would have one car and one BTC, you took a collateralized loan and you ended up with just the car.
There is no such thing as a bulletproof money-making scheme in which there is no chance of losing.
Let's not even mentioning the fact that you're entrusting your coins to a bank, in a Cyprus-style crisis this would be a thing to avoid.
I don't doubt that there are people taking loans not just for trading even as we speak but I don't think it will go anywhere to the scale of traditional loans.