This is correct for desktop and server. However, AMD hasn't said anything about the HEDT I/O die yet, as far as I know.
Assuming Zen 2-based Threadripper will still have quad channel memory and 64 PCIe lanes, AMD might go for a medium sized I/O die instead of disabling half of the large server I/O die. Or maybe the Threadripper volume is too low and a separate tapeout is not worth it.
I haven't seen a lot for Zen2 based Threadripper news since the end of May so maybe I missed how they are doing those chips like via the same 8 core chiplets as Zen2 or something larger. If their yields are really really good, maybe they are stacking 8 core chiplets for Rome and based on final yields on that determine what range will be offered as Zen2 TR HEDT to split 16 core Zen2 from Rome. Maybe at 16 cores, Zen2/Ryzen 9 is HEDT enough to compete?
If they are doing larger chiplets for Rome like 16 or 32 core but pairing up with Infinity Fabric for up to 64 cores, yields could also determine what becomes Zen2 TR with the weak chiplets becoming 8-32 core 92 chiplets), single CPU HEDT material? Or will they have a whole other solution here like limiting Zen2 TR to the same socket as previous gens to push upgrades vs a first gen TR user jumping to a Ryzen 3850X vs low end Rome?
This is true that they haven't actually confirmed that Threadripper is using the EPYC I/O die but I would be very surprised if it isn't. The entire idea behind Threadripper was to reuse as much EPYC tech as possible (in particular the physical socket) to keep NRE costs low because the HEDT market is so small.
Assuming Zen 2-based Threadripper will still have quad channel memory and 64 PCIe lanes, AMD might go for a medium sized I/O die instead of disabling half of the large server I/O die. Or maybe the Threadripper volume is too low and a separate tapeout is not worth it.