Seems to me its doesn't make sense to have a gov sell bonds in a currency that it doesn't have control of. This includes countries outside of the EU that use the Euro. When buying bonds of a country, there should mean the investor believes in the direction of the country / the governance there / believes it is low risk that the bonds would lose value or the strength of the economy would collapse. That's the risk that gets taken by the investor. It doesn't make sense to peg it to an external countries' performance. Of course it sweetens the deal but makes things confusing too.