My opinion: I think the rule may be a little too overbearing. Too hard to monitor, but also too hard for new owners/ owners that don't put a ton of time into the game to keep track of an ensure they are following. I believe a rule for the ST (like punt return) is needed. And also a rule for playing defensive players and offensive players on opposite sides of the ball. However, I feel this can be argued because players in real life have done it (ex. Deion Sanders). But these players are few and far between.
My biggest issue when I first read the proposal is that DL can't play LB, but LB can play defensive line. This seems counter-intuitive. Depending on what system you play, defensive players switch positions all the time in the NFL. I am a Titans fan in real life. Derrick Morgan is a recent example of this. In the 4-3 scheme they used to play he was a DE. But when they switched to 3-4 he was an LB.
IDK. I guess ultimately, I will support what the league decides on. I can honestly be swayed either way, but I feel we just need to worry about imposing rules to stop exploits as they occur instead of trying to restrict too much from the beginning.