Neat solution. At root, FX reserves exist to avert currency crises: when devaluation spirals out of control, dollars can be deployed to buy up the local currency. Asia, whose kitties were demonstrably not up to this task during the financial crisis of 1997-8, has learnt its lesson. Now some reserves in the region, which tot up to some $4,000bn, are arguably too big.
Conventional benchmarks, such as three to four months import cover or the equivalent of short-term external debt, take up a tiny portion of, say, China's $2,000bn booty. That is a blessing for the US, whose debt is now stashed in vaults from Beijing to Bangkok, but creates some rather unproductive assets for Asia.
Sure, certain central banks, for example in Russia and Korea, have been obliged to use reserves to support the currency. For the rest, however, bloated reserves now look more like a liability, especially if local currencies appreciate. Some, such as India, have already paid the cost through sterilisation bills: essentially paying more for the bills used to mop up local currency than they receive on US Treasuries.