How about they instead just penalise 'wrestling' like they should have from day one (thanks Storm)? We wouldn't even need the 6 again rule if they did that (go watch 80s/90s league and it's fast enough ffs).
E.G.
A)
2+ in the tackle? Check
Player in posession on ground? Check
Player being flipped onto their back/side after being put on ground? Check
= Penalty
B)
2+ in the tackle? Check
Tacklers hands pulling/ripping at the ball resulting in lost ball? Check
= Penalty
C)
2+ in the tackle? Check
Ball players movement stopped, opposition player attacks the legs? Check
= Penalty
If they're really desperate to 'speed up the game', change the 'kick for touch' option to a quick tap if penalty is given in opposition half.
Regarding head highs, they need to split it into two categories, intentional, not intentional... intentional = 10 in the bin/player sent off on the rare/terrible shots, not intentional (no serious injury) = penalty conceded, player fine.
PS also piss off the dead ball 7 tackle set, it's destroyed the long kicking game we all (most of us) fell in love with back in the day.