https://wccftech.com/rumor-amds-threadripper-3000-trx40-platform-may-not-be-backwards-compatible-after-all/

A rumor posted by ReHWolution's twitter account suggests that AMD's upcoming TRX40 motherboards which will house the Threadripper 3000 platform may not be backwards compatible with older Threadripper Gen 1 and Gen 2 processors and vice versa. This would be big news if true, because AMD has so far managed to retain its socket-agnostic philosophy when it comes to updating platforms. The reason why we think this rumor might have some merit is if you remember, we were the first to tell you of the existence of a 64-core Threadripper in the works a while back and this might necessitate some socket redesign.

AMD has been praised for being socket-agnostic for a very long time but it looks like a rapidly changing core-count and a shift to 7nm might force it to ditch the existing TR4 socket and move on to a new design for its TRX40 motherboards (assuming a tweet posted by an Italian publication turns out to be true). There could be multiple reasons for AMD to do this but the one most likely is that shifting to 7nm process technology requires a layout change (which in turn necesistated a socket redeisgn).