It's something that municipal bonds have made use of for a long time, and even was used to adjust their overall balance sheet by negating the outstanding defeased debt until a change a few years back. Basically, issue the bonds to borrow the money, and then, if interest rates have risen since the bonds' issuance, it was plausible to just buy a US Treasury bond that expired on or after the municipal issue, which either had a higher rate, or at least, enough of a larger quantity such that the interest income matched or outpaced the interest expense on the municipal issue. They required doing it with Treasuries just as they were deemed "risk free", but as we're not talking about doing this to take advantage of an accounting loophole, but actually address the nation's real economic position, doing it with Bitcoin would be quite sufficient to meet the needs, provided Bitcoin does what we all believe it will, and that it is purchased in enough size. Technically another alternative exists, depending on the the market prices, and that is, selling off the nation's resources to dispose of debt. This is basically the same strategy as accumulating Bitcoin, as at some point you do still need to part with some Bitcoin to pay off the creditors, but I would argue is more problematic for a nation. We can consider this the "sell your chairs" approach. Something tells me, though, that most Americans wouldn't be so fond of us selling the rights to Alaska's oil and forests, or the production capacity of the great plains, to dispose of the debt, however much we agree on the debt being problematic.