Limiting pit access is not the answer. Something to consider is that every event is different. I've been to competitions where pits are smaller and more cramped to others with very spacious aisles and pits and everything in between. I would be upset if my regional event limited pit access to x individuals per team when I could register for another event and have no restrictions. We can have about 6-8 people working in our pit (and contained in the 10x10 space) and have several more pit scouting or checking out other robots for their own enjoyment at any given time. It would also require a very organized and staffed volunteer system to put in place. I also don't the other xx individuals on my team feel excluded from the pits because they haven't been given the magical pass.
The answer is teams managing their team members. A proper pit manager (whether student, coach, mentor, etc) should make sure their team isn't spilling out of their pit and has a safe number of people. Everyone needs to police themselves to understand when they are needed in the pit area and when they are just in the way. Teams also need to design workable pit spaces. At every regional there are always those teams whose pit decorations and setup take up most of the 10x10 space meaning workers spill into the aisle and anyone who needs to ask a questions must do so from the aisle. Oddly enough those are also the teams with the most bodies around their pit areas. Oh well!
I think FIRST should have 1-2 volunteers per event whose job it is to walk around the pit and address traffic issues. If it becomes part of our culture to keep aisles clear we won't be having these problems.