I saw a very interesting seminar in 1999 telling how China and India will be the next global super economies in 30 years.
So 2029ish
Much sooner than 2029 - in fact global economies and currencies will be heavily redefined by new tech over the next 10 years, but as China "un-pegs" its currencies from the USD, and with the renminbi being approved as a global trading currency, and with the GBP losing some of its edge, we may see it sooner rather than later. However if it were to happen too quickly their economy would tank. It sounds counterintuitive, but it's the reality, as the biggest loser would be the USD, as other nations swap out USD reserves for renminbi, USD quickly depreciates. The largest single holder of USD is China through US Treasury bonds, which help to stabilise the currency appreciation on their end making it affordable for US to trade, and strengthens the People's Bank of China's global leverage, and local investment. But because of their pegging to the USD and fixed rate exchange control, the currency has never been globally trade-able to much of an extent and the central bank's meddling in economic policy to maintain the artificial pegging rates causes problems even if you held the currency. But as they "un-peg or de-peg" from the USD by selling off treasuries and expanding their reserves, their new renminbi becomes a very viable global currency and is preferred over the USD due to the better stability offered by the economy underlying it than the United States which may have breached its tipping point in its debit positions.
As the renminbi expands its base issue products into a wider array of bonds, contracts, and derivatives, it becomes a far better buy for foreign reserve banks in EU (incl UK) than the USD-issued products or GBP-issued products, especially with local trading hubs across the world which the IMF have facilitated. If Beijing just relinquished a little control over its monetary influence and welcomed true global pricing risk without posing risk to those buyers, they'd springboard over the USD fairly quickly as the renminbi has a better value proposition across the board, in the long-term. It's one of the reasons Nigeria, for example, experienced such an economic boost in recent times as they've already made the switch. But Beijing is worried about placing trust in market-based pricing and the subsequent influence other nations have over their economy, so it's a slow game of attrition against the USD for now. Until the Middle East begins to price oil in renminbi and you'll find the hedge product buyers switch over quickly too, and a run against the USD will scare others into the safety of renminbi. Or China devalues again to maintain the Yuan peg price and it could fail before it even really gets a chance - it's up to Beijing.
India has a well educated population willing to work for peanuts. They have a huge economy and an even larger economic opportunity...