No country wants to be the first one to do this, and unilateral action could cause panic in other countries à la Russia. What is needed is a system that involves cooperation between the host country, private lenders and the IMF. We saw an example of how effective this can be for Korean bank-to-bank debt late last year.
Ideally, this should not be on an ad hoc basis, as it was in Korea, but should be thought out well in advance, with the possibility of such workouts included in loan documentation. This, of course, would increase the cost of borrowing by emerging market economies, but that would be no bad thing.