Issue with that is the player recovers and then what? You have a fit player not playing.It was my understanding it's an injury sub, not just concussion sub. Anyhow agree simplest solution is forcing subbed player to miss the following week, including finals/grand final
Some injuries can be misdiagnosed, others can be recovered. E.g. they might sub you out with a rolled ankle where you can't run on it, but a week of RICE and a jab before the next game and you can play.
I think the easiest solution is to just call it a sub, and you can do with it what you will.