I doubt that all motherboards will have all issues fixed as manufacturers have released one quick update and now try to focus on Z270 boards. What more most KL BIOS releases for Z170 were about a month before KL premiere.
ASUS ROG has better support and I guess that ASRock as always will try to fix all the can but I have my doubts in Gigabyte or some less popular and cheaper MSI or ASUS boards.
Most updates for Z170 motherboards which I was checking look like 5-10 releases, 3-6 months nothing, KL update, 1 month+ nothing. Even boards like ASRock OC Formula have only 1 update with KL support since about March last year.