I wouldn't be surprised if we get guidance / philosophy similar to hits near the sideline. On sideline hits, the ball carrier must have a foot down in the white or clearly giving himself up heading OOB for a PF UNR or late hit foul.
In the sliding QB play here, no TGT IMO, and the lateness of the slide puts the ball carrier at risk of receiving a legal hit, which I think we have here. If that player started his slide even a second earlier, that would give the defender enough time and distance to recognize and avoid contact. If he didn't, then we have a PF late hit / piling on, same as always.
Regarding the helmet coming off, we've all seen wrap up tackles on RBs or WRs where a helmet comes off and there was no FMM. It does happen, and this is still a contact sport. If player protection is the goal for the sliding ball carrier, coach the players to get down earlier.