With the 7nm fabrication process, AMD has been able to double their core count on the mainstream Ryzen line-up using the AM4 socket. With the announcement of the Ryzen 9 3950X, the current 2950X Threadripper looks redundant.
So it will probably come as no surprise that the new Threadripper chips will continue the trend of massively upping the core count and an AMD are planning a monster 64-core Threadripper.
Apparantly, the new HEDT platform is currently called X599 but it is claimed this will change names by launch, to reduce confusion with Intel.
The current belief is that the socket will not change so the new chips should still be cross-compatible with the older X399 motherboard and only a bios update should be needed if you already own one.
While the Ryzen 3000 chips use the 7nm fabrication process, it is possible, if not likely, that AMD will retain the 14nm process for these new chips. The physical size of TR4 allows them to fit more chiplets on, and these chips are will be based on the same technologies used in the EPYC Server CPU range.
There is no word on pricing, at the moment the best guess is in the $2500 to $3000 range which will still make it appealing over the Intel HEDT range or the more expensive server options.
The current timescale is apparently aiming to ship around mid-Q4 2019 but as late as January 2020. They don't want to go over this time frame as they have other things planned for CES 2019.