In theory, I think SDRs could be used successfully; however, the problem is with the economic size of the nations involved and pre-existing debts. For instance, The US is part of the IMF's SDR program. The US wants China on board. China wants no part because of the debt it holds of the US'. If all nations (hypothetically) were to transition into SDRs, existing debt obligations would be buried.

Countries in heavy debt want this, countries with no global debt don't.

Conversely, countries with "lots of money" (countries in debt like the US) are expected to buy SDRs in a larger portion to help smaller countries get loans from the IMF or a more favorable exchange rate for their currency. Countries with no money (who want cheap credit) are expected to go to the IMF for loans. De facto they are under the control of the IMF and wealthy nation participants (not really different from today).

The current SDR system in place through the IMF is having the same problems the US is having now regarding being the world's reserve. Nobody wants to give up the power associated with having reserve status. All the solutions are the same (currently). If it's not a nation, it's a bank. If it's not a bank, it's an entity. If not an entity, it's a government.

Nations in heavy debt are screwed (i.e. the US), but the US can self sustain with it's political power and military might in the world. Europe is partially screwed, but has a socialist net that will keep default states afloat because it's in the interest of all intertwined.

The fairest solution of all (IMO) would be to let nations form agreements for their global trades. No need for a reserve to set the standard. There is no standard, only what nations negotiate. I do understand this may bring "unwelcome" bargaining in the dark areas of the markets for arms and such, but this happens anyway. The world isn't fair, it's survival of the fittest.