Custom gamerpics are currently being tested for use on Xbox according to a Reddit post by Major Nelson. The new feature is currently available to Alpha build members of the Xbox one Insider program who have been hitting Twitter already to show off their designs, including one Xbox Corporate Vice President, Mike Ybarra.
— Mike Ybarra (@XboxQwik) April 12, 2017
The ability to design your own gamerpics had been one of the most requested dashboard features for quite some time, though it is likely to be in kept to the Preview program for a while longer before rolling out to everyone.
Source: Major Nelson via Reddit