We used full face helmets in Kyokushin and punched to the head. It was something that started in Japan when K1 became popular back then Andy Hug was still alive.(Mid to Late 90s)
You would still have the bare knuckle aspect of normal knock-down fight but you could punch in the head. We just wore full face helmets a little like Wing Chun does.
Later when I changed to Ashihara we trained both knock-down and also more Muay Thai style fighting with Boxing Gloves. In the end even ground fighting was included into the Ashihara training having several jujitsu instructors helping out.
Most styles that are full contact will adapt to the new fighting trends (like MMA). If you take Pride, or K1 you will see several ex Kyokushin style (Knock-Down style) fighters.
PS: I assure you the no punching to the face is not to protect the hands but to protect the heads