The Rules.
I can go on and on about the rules and regulations of this great sport we call football. The rules matter, how they are enforced and adjudicated matter, and how they are created matters. Rulebooks should have some fluidity as they should be changed when needed. However, they also should not be changed all the time or changed just for the sake of change.
One of the biggest differences between the Brand New Shield and the NFL will be the processes in regards to creating and amending the rulebook. There will not be a couple committees who meet in posh locations a couple times a year with the most expensive food money can buy on the table. Let's get that out of the way first. There will also not be these weird votes on rules that are only among some extremely wealthy owners without others involved having a say. There needs to be a strong collaborative effort to create a rulebook that can be officiated and adjudicated by the refs both on the field and in the booth. Yes, there will be at least one ref in the booth during games of the Brand New Shield should games actually happen.
Honestly, the NFL Rulebook is one of the worst rulebooks ever written. It is filled with redundancy, ambiguity, rules that have exceptions that have exceptions that default back to the original rule, and of course some outright contradictions. I'm not going to go into all my gripes here, I just wanted to paint a general picture of what the problem is. The way the rulebook is written puts players, coaches, and the officials all at a disadvantage. Rulebooks should be as clear, concise, and objective as possible. The NFL Rulebook is none of those things.
One of the things that would make things better is to make challenges universal. Anything can be challenged, but you only have two challenges, which is very similar to how it works in the CFL. Making everything reviewable ensures that the game gets officiated and adjudicated correctly. Creating processes to make sure that challenges and reviews are handled efficiently and effectively is crucial to the success of any football league.
Using technology to assist officials is something else I have advocated for. Some kind of iterative offline technology with camera assistance could definitely be a boon for sports as a whole. It would have to be implemented correctly, but anything that improves officiating should be looked at and considered.
In conclusion, a better rulebook, officials in the booth in addition to on the field, and using technology to assist the officials when needed would all greatly improve the football experience.