While it is always tough receiving a red card, the combination of increased player strength and the nature of the contacts leave the lawmakers little choice. I would however be an advocate of returning to rucking as it once was, there was only risk when players got onto the wrong side and got a shoeing for their troubles. It would remove the role of the jackal with all the risk that they have, as any form of neck roll or even crocodile roll is of no value. I also preferred old fashioned scrum engagement as less likely to cause injury to front rows. Remove substitutes at will as well and the game starts to have a more even match up in the tackle in terms of player fatigue. Or we just play sevens.
Some good challenges here. Rules makers have to always look beyond the immediate effect and consider what knock-on effects there will be in the game. FWIW I think Rugby lawmakers are better than most sports in this (and decades ahead of the inept FIFA). However the large number of substitutes has encouraged a serious bulking up of players, plus given them the chance to sub a tired player off. The net result is harder hits. It feels like there are more injuries as well - difficult to guess as accurate number, but perhaps 1.5 players per side being subbed off with an injury?
Solutions will be harder, and a complete abandoning of substitutes would in the short term see games decided by those that avoid injury the best. Not ideal for sure.
For me, the focus must be around reducing the short sharp head to head contacts and as well as the issues around the ruck, I'd also want to find a way to reduce the volume of close quarters pick & go moves. Not only are they a major risk for concussion, they're also dull as a spectacle. It's not easy to see the answer, as the consequences would have to be thought through (and trialled). Reducing the subs to (injury?) subs of a prop, loose forward and a single back might help, and props / hookers would once again be asked to train to cover other positions in the front row.
The overall aim of such changes would be to make gaps through tiredness of defences more prevalent, which would force teams to forego bulk in favour of broader athleticism and stamina. A faster game with fewer close quarter hits.
This feels a more natural way to address the issues, rather than trying to restrict the possession time of each attack, as surely that would end up with more kicking (another problem in the game), plus making it feel more artificial. Plus removing the possibility of a 25 phase attack going from one end of the pitch to the other would feel a genuine loss.