Here's a little something coming up in next version of CK2+: A new loan system!
I always thought loans were a bit lackluster in their implementation in vanilla. First of all, the loan size is the same regardless of whether your income is 1 or 100. Secondly, the event doesn't fire until you're deep enough in the red for your mercenaries to be gone and your armies broken. Finally, it felt a little weird that you could escape your debt through a timely death.
In the new loan system, you have complete control over when you take a loan. Doing so is done through a decision, with a loan sum that scales to your income, so it is never too little to be useful or too much for you to pay back. The interest is fixed at 25%, so loans are worth taking even if your stewardship happens to be low.
Five years after taking the loan, it will come due for repayment. If you have the cash on hand, you can of course just pay it back...
... but if you do not, there's a few options. If you have enough money to pay the interest, you can put that down and extend the loan for another five-year period, although naturally this means paying more money in total than if you just repaid it the first time around.
If you happen to be completely broke, you can simply ask for more time. This will extend the loan for five years, although you will lose prestige equal to the cost of the interest.
Of course, you can also just tell the moneylenders to get lost, but doing so will have consequenses.
And finally, if you thought death was the end of your debts... think again.
In addition to the benefits the new system provides to the player, it will also be fully utilized by the AI, who will take loans during wartime to fund mercenaries and maintain their troops.