You can't write off the debt that is hold by foreign investors, but you can write off the debt that is hold by central banks, but will that action hurt anyone?
Central bank is always net plus since they create money and lend those money out (the ownership of those money belongs to FED directly after being created)
If the central bank is really controlled by the government, like some people believe, then they have no problem to destroy the bond they purchased from government, means that they just freely give those printed money to government without asking anything for return
Currently FED are buying 40 billion dollar worth of bonds from government each month(with newly created money). If they just destroy those bonds, then government will get 40 billion dollar free money to spend each month. I don't see any problem with this. Of course there will be a loss from central bank's balance sheet (now they have liabilities without corresponding asset), but since they are the money creator, they don't lose anything
On the other hand, if government get free money to spend, they will spend a lot and create lots of jobs
Actually this practice was done 300 years ago by John Law. He first printed out lots of fiat money and use those money to raise the stock price of mississipi company, and then used those stocks to buy back lots of government bonds and then destroied those bonds, thus helped the government to eliminate the national debt
His faliure is caused by the fact that he printed too much money to raise the stock price of mississipi company, and he could not provide enough gold backing those fiat, thus resulted in a bankrun. But today, FED don't need gold to back the fiat