Yeah, but will they enforce it
I want nothing to do with any changes that involve officials judgement. It simply needs to be procedural. If the refs have to stop the game for an injury X is what happens. Here is my current thoughts.
Maybe get one free one per half, but lose that one once inside 4 minutes of each half.
Don't want penalty yardage involved. If a defensive player goes down and requires an injury timeout, let the play stand, spot the ball and give the down back to the offense. As for the player(s), if they go down and a stoppage is required, a member of the medical staff must come on the field, and unless a player safety issue, the helmet is to be taken by an official who will afix a tag defining the reentry time for the play, I like 3-5 minutes, and give it to the medical guys who are required to hold the helmet just like they already do for concussion protocol. That calculation will go across any period break, not sure how to deal with OT yet, maybe first OT at end of regulation or including next OT if in OT. If the offense does not substitute, then the only sub allowed is for the injured player. Offensive team has the option to start the clock on the ready or at the snap. This can all be mitigated if the team has and wishes to use a team timeout that would have stopped the clock anyway. Won't eliminate trying to stop momentum, but it will have a cost.
If not 3-5 minutes, it needs to some significant number. Sitting out one play is nothing, since the LB that wanted to get out and replaced by a nickle is the most likely offender. Same for a run stopper needing to be replaced by an edge rusher. Play the safety first card and go big. The player should at least be required to enter the cute little injury tent. Cramps will go down, and some real ones will hop off the field. Real injuries need to be addressed.
Have not really thought through offensive side yet. Maybe applying penalty type clock runoff rules would do, but think sub restrictions on that side should be considered during a running game clock. What better way to stop the clock and get the Hail Mary or short yardage teams out there during short clock situations.. Once again use of a timeout heals the situation.
But take the judgment out of the hands of the officials and replay real time. If the league wants to review suspicious activity after the fact, go for it. But that might need more review time real time and that needs to be avoided.
I am sure I short sighted some issues, but this is a start that I think COULD be fair and effective and all the refs have to do is follow the procedures.