How would you emulate what happened to England in the 18th century when their war debt was about to bury them and they had to turn to one of history's greatest scoundrels to find a way to bail them out? Is there a way to put a John Blunt style event in the game to emulate the South Seas Company situation, where a massive amount of debt was about to come due, and a great scoundrel makes a lot of profit moving the debt around, fleeces millions including the King, but actually also saves the nation's finances by allowing them to defer the debt payments?
So if your total debt rises to a certain multiple of overall income, a private banker arrives with a scheme to defer or refinance the debt, and each time he appears he gives you a new option to allow you to defer your debt (reduced interest, moves the date for repayment of the debt further down the road) for a very "reasonable" concession on your part, some of which even benefits you in the short term, maybe it increases Mercantilism or Burgher favor each time as well as a small cost in monarch points, a slight kick upwards to Inflation, and the deferral of the debt.
Then, if you haven't paid off over a 10 year event cycle, the chain culmantes in a collapse of the "bubble," with some really hideous maluses if you haven't paid the debt off in the meantime? Something like -3 stab, +10 inflation, and your relationship with the Burghers going right in the tank tipping off the prospect of a burgher revolt disaster? Something like that. I'm no modding genius but I think that could work and would be a fascinating narrative event chain.