Found PR for new X299 board with support for only Kabylake X and no support for Skylake X.
https://www.overclock3d.net/news/cp...aunches_a_kaby_lake-x_only_x299_motherboard/1
https://www.overclock3d.net/news/cp...aunches_a_kaby_lake-x_only_x299_motherboard/1