No matter the current favourable situation, taking the loan to buy the Bitcoin is no good idea.
First rule of investing is that you invest extra money that you don't need and not to invest money that you don't have.
Bitcoin is volatile and price changes, there is always possiblity that you will lose and not be able to return the loss or that will cost you a lot. So, always bare that in mind before making decision to take the loan.
To be fair, that "rule" is the bad "rule". If you aren't a rich person, then you'll never have a business if we follow that rule cause business requires high investment. That rule is probably good at gambling. You succeed when you invest more than you can afford. Usually, the higher the risk, the higher the potential reward.
Loan to buy a bitcoin is a risky investment but again, reward is very high. If you get a loan for one year with 10% rate and invest in bitcoin, there are two possibilities: 1. Price of bitcoin will go down or stay the same, according to price, you'll have to pay invested bitcoins + rest of the money. 2. If bitcoin's price goes up, depends on the percentage, you may pay that loan and get 1x, 2x and higher amount of money.
1. If you've got $1000 loan in 2011 and bought bitcoins, you would be very rich. But if you've got a loan when the price was 20K, then you would be poor.