Because we have only had 4 recognised belts in modern times, there are only two fighters that have held all 4 belts at the same time, first it was bhop, then Taylor. Who will be the next?
Jermain Taylor, and Bhop who he won the belts off of, are the only two boxers who have been undisputed in the 4 world title era since 2005. Right now, only GGG and Kovalev have a realistic chance of becoming undisputed in 2017 with GGG potentially getting his 4th belt by the end of 2016.