> What is in the SDR is public information, so if you wanted to track them, it's not that hard.

The problem is the contents of the basket changes every 5 years. It is trivial to build your own “emulated SDR” just by holding appropriate amounts of the underlying currencies; but the problem is that in 2027 the IMF is scheduled to change the weights of the basket again; that means you may have to execute some (potentially very big) currency transactions to rebalance your “emulated SDR” to match the real one, and there’s a risk you won’t be able to do so at the rates the IMF assumed when it decreed the reweighting, especially since it doesn’t use spot rates, it uses 3 month average rates.

One option is to treat each edition of the SDR as a separate currency, so you might offer 2022 SDR and 2016 SDR in parallel. Another would be to have your “eSDR” aim to converge to parity with the SDR in the long-run, but allow it to temporarily deviate from parity whenever the basket updates.

SDR issued by the IMF don’t have this problem-whenever the definition changes, they all update accordingly-they are to a certain degree a “fiat” currency. There are two problems though-the first is that only sovereign states and certain international organisations established by treaty are legally allowed to possess them, private individuals and companies cannot. Some would like the IMF to change the rules to allow private ownership, but the US always blocks that because they are afraid of the SDR competing with the USD as the de facto global currency-and the IMF’s rules were architected to give the US a veto over all major decisions. The second issue: if you legally own SDR, you can take them to the IMF and ask to swap them (e.g.) for USD, and the IMF will work with the US Fed to ensure the transaction happens at the current official USD-SDR exchange rate. The problem is, the IMF rules only let holders carry out these transactions under quite restrictive conditions, meaning the SDR isn’t in practice freely convertible with its basket currencies-again, the IMF could loosen those rules, but the US would likely veto it.

Ultimately, some kind of private edition-based SDR emulation, or even a continuous emulation which closely tracks the SDR but temporarily diverges from it around reweighting time, is entirely feasible for a private actor (such as a bank or ETF issuer) to issue. I think the main reason why they don’t, is there just isn’t market demand for it - and an emulated SDR issued by a private actor is potentially at the regulatory mercy of the country to which that private issuer belongs, to a much greater extent than real SDRs would be.

It’s not that crazy, nearly every USD stablecoin has the same problem.

It does turn you into a bank during the transition period though where you may not be able to redeem all deposits at once.