I know its a quaint notion, but this rule would not be necessary if kids committed to the school and not to coaches. Not allowing kids to transfer to the location of the new coach will curtail a lot of the mass exodus fear, but this like any change is loaded with potential issues.
Let's say you are a mobile, dual-threat QB who committed to a coach that was going to run a system that worked well with your abilities. Then that coach leaves after your redshirt year for another school and is replaced by someone who wants a pro-style passing game and you have a very limited future. Does that seem fair to you?
Same thing in reverse - you're a WR with deep threat speed but after a coaching change, you now spend all your time blocking because you've become a triple option team.
On top of that, the "school" you commit to only gives you one year scholarships and they can essentially dump you at the end of any given year. And they can prevent you from choosing another school if they want - does that sound fair to the kids?
Those are extreme examples but we've all seen cases where a coaching change led to some players becoming nailed to the bench for some reason. The Big 12 proposed solution is the closest thing I've seen to an answer to many of the problems without just going to 100% free agency.