Currency is still fluctuating as the Chinese yuan has weakened enough to eliminate projected nominal GDP gains in 2016.
IMF nominal GDP projections
Purchasing power parity had a large adjustment a few years ago because the 2005 PPP study did not properly look at or weight the rural areas of China and India and other developing countries. This meant that purchasing power was a lot higher in developing countries.
Their could still be some adjustments in how GDP is accounted and purchasing power corrections but it seems that any adjustments will be a lot smaller.
In purchasing power parity GDP China will be at 120% of the US economy in 2017 and the IMF is projecting that China will gain about 5% each year. IMF projects China would be at 140% of the US economy in 2021.
China is at 60% of the US economy in nominal GDP terms (currency exchange basis). Currency moves will shift the GDP ratios around more than PPP.
India will be at 40% of the GDP of the USA and will gain about 5.5 percentage points on the US. IMF projects India to be at 62% of the US PPP GDP in 2021.
Japan is at 21% of the US economy PPP GDP wise and sliding to 15.8%
Germany is at 17.6% and UK and France are at 12%. Each of the european countries will grow less than the USA.
By 2029 or 2032, China should be double the economy of the USA in PPP GDP.
At some point it seems likely that the yuan will strengthen again versus the US dollar. The US dollar is currently very strong against all currencies.
IMF PPP GDP projections for 2020 and 2021
SOURCES- IMF, Wikipedia