Saw this blurb at Guru3d from a twitter post:
Ryzen 3000 processors could very well support 5000 MHz DDR4 memory 
Yuri Bubliy, also known as from 1usmus from the Ryzen DRAM Calculator posted on his Twitter feed that upcoming processors will support memory at a speed of 5,000 MHz.
A few days ago more specs already leaked indicating that a 16-core version indeed is in the works for AMDs 7nm fabricated processor line. He states that Ryzen 3000 could be able to manage very fast DDR4 memory, even up-to 5000 MHz. While that is a super high (and expensive) DDR4 memory clock frequency, we do know that Ryzen always has preferred fast memory for a multitude of reasons.
Bubily mentions that the UClk, the controller's clock speed, is equal to half the module. A module of 5000 MT/s, therefore, has an effective clock speed of 2500 MHz, so the controller should, therefore, achieve a speed of 1250 MHz.
