ASRock's X299-ITX/ac is a decent choice to build a tiny system with, offering a wide variety of features as well as the ability to trim some of them off if you do not need them. There are two removable PCBs, one which holds the SATA ports as well as a USB 2.0 and a USB 3.0 header while the second carries the LAN chips, a USB hub and your M.2 slots. There may be cases in which removing one or the other makes room for other equipment in your enclosure, with the option to add them back later on. You can see how the ~$400 board performs at TechPowerUp.
"ASRock's X299-ITX/ac is that mini motherboard for Intel's X299 platform that takes all that is good and shoves it into a board smaller than a shoebox. With a triplet of M.2 ports and dual LAN chips, plus Wi-Fi, there's almost nothing missed, other than some PCIe slots, making this board an engineering feat only ASRock could accomplish."
Here are some more Motherboard articles from around the web:
- ASUS ROG Maximus X Formula @ Guru of 3D
- AORUS Z370 Gaming 7 @ Modders-Inc
- Gigabyte Z370N WIFI Mini-ITX @ Guru of 3D
- Biostar Racing Z370GT6 @ TechPowerUp