Today many lga1151 motherboards have announced bios updates to support the upcoming kaby lake processors.
Microsoft has said that windows 10 will be needed to support kaby lake.
I suspect that statement is misleading; Microsoft wants to push all to windows 10.
If you are on windows 7, I suspect you will run kaby lake as well as you run a skylake processor today.
What you might miss out on is the fast switching power capabilities or other such kaby lake improvements.
Similarly, the new kaby lake chipset motherboards will likely support skylake processors.
I could be wrong.
But those who know are under NDA and those who tell are just guessing.