the thing is, if you want to buy a new pc now, then get it now.
if you're getting one for Christmas, then review the matter in november.
I agree that kaby lake will probably not be worth it. I assume 100-200MHz more stock clock, maybe better boost clocks, probably better efficiency, but nothing big and considering the price (which I assume will be ridiculous upon release) the 6700k will do fine
however the Z270 boards could be interesting. but again, if your pc is dying now, get a new one now. I can't imagine a Z170 board going out of date in the next 4 years.