US finance still dancing to the wrong song?

Charles Prince, former Citigroup CEO famously explained his bank's actions in July, 2007 thus: "As long as the music is playing, you've got to get up and dance." I feel very much with that recent era in mind, Gillian Tett at the FT asks a very provocative question: "Could sovereign debt be the new subprime?"

If this is a bit outside your expertise, the question is basically, Banks are being forced to buy tons of government debt (bonds) because they are supposedly super-safe assets, but why should we assume that they will remain so and what happens if they're not? It's a scary question, b/c this sort of "perpetual" motion machine of super low central bank rates financing a ton of sovereign bond purchases is the current foundation of both the US government's borrowing and the American banks' recovery- but it's hard to say what happens when the music stops.