While Intel is no longer supporting Windows 7 with its 200-series chipsets for Kaby Lake, it seems AMD is hard at work to add Windows 7 support for its new Socket AM4 motherboards.
If the information is correct, motherboards based on the A320, B350 and X370 chipsets will support Windows 7.
Personally, I'm not sure if this is worth the effort. It does not make any sense to stick with the more than seven years old Windows 7 if you're going to buy a new motherboard plus processor. AMD will score some karma points here and there but it's time to upgrade to Windows 10 to enjoy all its modern features and better security.