Building a currency basket is always challenging, so we will try to look for different benchmarks. But this is not an easy task. For instance, the Central Bank of China keeps the percentage of the different currencies of their reserves in secret (that would be a really good benchmark!).
One of the most famous currecy baskets is the SDR (Special Drawing Rights) designed by the IMF. In November 2015, they are holding the following currencies: USD 48%, EUR 33%, JPY 7%, and GBP 12%. For sure, before the end of 2016, the Chinese currency, RMB, will be included and, later on, the oil will be priced in SDR.
Another possible benchmark is COFER (Currency Composition of Official Foreign Exchange Reserves). You can find its portfolio here.
Be prepared: some Arab countries with currecies pegged to the USD might break the peg and follow Kuwait's example and start a new peg with a basket of currencies. Another option is simply devaluing their currency against the USD.
Also some other countries are increasing the amount of gold in reserves just for diversification (consider gold as another currency in the portfolio).
Probably, in the years to come, the USD won't lose its privileged position, but it will be reduced and effectively swapped by SDR, which includes USD as the main currency.