We have not yet seen any mini-ITX platforms with Threadripper support, but ASRock is now doing us one better with it's proprietary Deep mini-iTX form-factor motherboards supporting server-grade AMD EPYC Rome CPUs with up to 64 cores and 128 threads.
https://www.notebookcheck.net/Server-grade-mini-PCs-ASRock-reveals-Deep-mini-ITX-motherboards-with-AMD-EPYC-Rome-CPU-support.506212.0.html