z97 Extreme6 + windows 10?

What Xaltar said is absolutely correct. The hardware on the motherboards  was purchased from other MFG's, so you can't ask if asrock will prepare drivers when they only make the board and app software.   Windows 10 is not like windows 8 where the BIOS / UEFI needed an update to run the new OS stable. The The Kernel in windows 10 has not been changed so much that it will be needed to run a stable win 10.   Realtek sound already has win 10 drivers out and some Lan.  The AHCI and RAID drivers from Intel for win 8.1 have been fine with all the windows 10 insider previews.  Z97  INF chipset installer, the Intel lan 218.  Nvidia  has win 10 drivers.  Windows 10 has embedded drivers that work for most of the old and newest hardware but not too old.  

I think its safe to say that there will be windows 10 drivers for most, if not all more recent boards. Most of the drivers for Asrock, and any other brand motherboad, are provided by other vendors like chipset by intel, sound by Realtek etc. So long as the components receive new drivers from their specific vendors they should become available.