The latest Threadripper rumor is not a good one for those who enjoy backward compatibility. In a post at overclock.net, DRAM Calculator author Yuri Bubily (1usmus) claims that third-gen Ryzen Threadripper CPUs will not work on X399 boards.
It may also be the reason why AMD delayed the processors and removed them from previous roadmaps. “HEDT disappeared from all calendars and the release of these processors was forced to postpone.”
Since the new processor has a new memory controller and he in a single copy (instead of two as before) had to seriously change the pins. Also, the new PCI Gen 4 standard and new power pins made a special contribution. TRX40 and TRX80 are a new generation and a new architecture. Nothing to do with the past generation.