nobody other than the kicker or returners are allowed to move until the ball is either caught or dropped. There would be no need for a fair catch under those circumstances since the returner would never be in any danger. It would always be in the receiving team's interest to try to return the ball.
Moving the touchback up to 30 yards also provides an additional disincentive for the kicking team to just boot the ball out the back of the end zone every time. You'll probably see a lot more caught kickoffs with run-back attempts under this new rule, but the receiving team will still have to work hard to get an advantage on the return, because the kicking team will be lining up on the receiving team's 40 yard line, which doesn't give them a lot of room to run.
It's almost like kickoffs are now short-field punts with a guaranteed catch. The kicker will try to pin the returner back near the goal line, and it will be up to the returner whether to catch it and go or hope it rolls into the end zone for a touchback.
It's a radical change but I'm kinda curious to see how it plays out.